Influence of thermal and resonance neutron on fast neutron flux measurement by super(239)Pu fission chamber

The super(239)Pu fission chambers are widely used to measure fission spectrum neutron flux due to a flat response to fast neutrons. However, in the meantime the resonance and thermal neutrons can cause a significant influence on the measurement if they are moderated, which could be eliminated by usi...

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Bibliographic Details
Published in:Chinese physics C 2015-01, Vol.39 (1), p.016001-1-016001-4
Main Authors: Zeng, Li-Na, Wang, Qiang, Song, Ling-Li, Zheng, Chun
Format: Article
Language:English
Subjects:
Assembly
Chambers
Cross sections
Fast neutrons
Fission
Neutron flux
Polyethylenes
Spectra
Online Access:Get full text
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Summary:The super(239)Pu fission chambers are widely used to measure fission spectrum neutron flux due to a flat response to fast neutrons. However, in the meantime the resonance and thermal neutrons can cause a significant influence on the measurement if they are moderated, which could be eliminated by using super(10)B and Cd covers. At a column enriched uranium fast neutron critical assembly, the fission reaction rates of super(239)Pu are measured as 1.791x10 super(-16), 2.350x10 super(-16) and 1.385 x10 super(-15) per second for 15 mm thick super(10)B cover, 0.5 mm thick Cd cover, and no cover respectively, while the fission reaction rate of super(239)Pu is rapidly increased to 2.569x 10 super(-14) for a 20 mm thick polythene covering fission chamber. The average super(239)Pu fission cross-section of thermal and resonance neutrons is calculated to be 500 b and 24.95 b with the assumption of 1/v and 1/E spectra respectively, then thermal, resonance and fast neutron flux are achieved to be 2.30x10 super(6), 2.24x10 super(6) and 1.04x10 super(8) cm super(-2) times s super(-1).
ISSN:1674-1137
DOI:10.1088/1674-1137/39/1/016001