Neutron angular distribution in plutonium-240 spontaneous fission

Nuclear safeguards applications require accurate fission models that exhibit prompt neutron anisotropy. In the laboratory reference frame, an anisotropic neutron angular distribution is observed because prompt fission neutrons carry momentum from fully accelerated fission fragments. A liquid organic...

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Bibliographic Details
Published in:Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Accelerators, spectrometers, detectors and associated equipment, 2016-09, Vol.830 (C), p.163-169
Main Authors: Marcath, Matthew J., Shin, Tony H., Clarke, Shaun D., Peerani, Paolo, Pozzi, Sara A.
Format: Article
Language:English
Subjects:
Fission neutron anisotropy
INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
MCNPX-PoliMi
NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL PROTECTION
Nuclear safeguards
Plutonium
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Summary:Nuclear safeguards applications require accurate fission models that exhibit prompt neutron anisotropy. In the laboratory reference frame, an anisotropic neutron angular distribution is observed because prompt fission neutrons carry momentum from fully accelerated fission fragments. A liquid organic scintillation detector array was used with pulse shape discrimination techniques to produce neutron-neutron cross-correlation time distributions and angular distributions from spontaneous fission in a 252Cf, a 0.84g 240Pueff metal, and a 1.63g 240Pueff metal sample. The effect of cross-talk, estimated with MCNPX-PoliMi simulations, is removed from neutron-neutron coincidences as a function of the angle between detector pairs. Fewer coincidences were observed at detector angles near 90°, relative to higher and lower detector angles. As light output threshold increases, the observed anisotropy increases due to spectral effects arising from fission fragment momentum transfer to emitted neutrons. Stronger anisotropy was observed in Cf-252 spontaneous fission prompt neutrons than in Pu-240 neutrons. •Pu-240 prompt fission fast-neutron anisotropy was quantified for the first time.•MCNPX-PoliMi and MPPost codes were used to remove cross-talk neutron detections from experiment results.•Cf-252 spontaneous fission neutrons were found to be more anisotropic than Pu-240 neutrons.
ISSN:0168-9002
1872-9576
DOI:10.1016/j.nima.2016.05.064