Prompt Neutron Decay Constant from Feynman Variance Fitting

Conference · Thu Jul 16 04:00:00 EDT 2009

OSTI ID:970890

McConchie, Seth M. ^[1]; Hausladen, Paul ^[1]; Mihalczo, John T. ^[1]

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1. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

The use of fast-response liquid scintillators for passive measurements with highly enriched uranium (HEU) castings provides information on the timescale of the fission chain multiplication process for HEU. Thus, these detectors produce time responses characteristic of the HEU and not the moderator around 3He counters. Up to five HEU castings were assembled, and the passive time coincidence measurements performed. The prompt neutron decay constants inferred from the Feynman variance data with the arrays of large liquid scintillators are compared with decay constants obtained from previously presented Feynman variance data collected in active interrogation measurements with these same HEU castings. The active measurements used plastic scintillation detectors adjacent to the castings to eliminate time-of-flight effects and showed that the prompt neutron decay constant is clearly not exponential. However, time-of-flight effects in the passive measurements result in exponential behavior and allow the Feynman variance data to be fit with the well-known point kinetics analytical formula. The characterization of the prompt neutron decay constant is investigated by comparing the results of the passive and active measurement data.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA), Nuclear Criticality Safety Program (NCSP)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 970890
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
CASTINGS
CHAINS
Comparisions
DECAY
FISSION
Fast-Response Liquid Scintillators
HIGHLY ENRICHED URANIUM
Highly Enriched Uranium (HEU) Castings
KINETICS
LIQUID SCINTILLATORS
MODERATORS
Nuclear Criticality Safety Program (NCSP)
PLASTIC SCINTILLATION DETECTORS
PROMPT NEUTRONS
Results