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Title: Characterization of Fissile Assemblies Using Low-Efficiency Detection Systems

Here, we have investigated the possibility that the amount, chemical form, multiplication, and shape of the fissile material in an assembly can be passively assayed using scintillator detection systems by only measuring the fast neutron pulse height distribution and distribution of time intervals Δt between fast neutrons. We have previously demonstrated that the alpha-ratio can be obtained from the observed pulse height distribution for fast neutrons. In this paper we report that we report that when the distribution of time intervals is plotted as a function of logΔt, the position of the correlated neutron peak is nearly independent of detector efficiency and determines the internal relaxation rate for fast neutrons. If this information is combined with knowledge of the alpha-ratio, then the position of the minimum between the correlated and uncorrelated peaks can be used to rapidly estimate the mass, multiplication, and shape of fissile material. This method does not require a priori knowledge of either the efficiency for neutron detection or the alpha-ratio. Although our method neglects 3-neutron correlations, we have used previously obtained experimental data for metallic and oxide forms of Pu to demonstrate that our method yields good estimates for multiplications as large as 2, and thatmore » the only constraint on detector efficiency/observation time is that a peak in the interval time distribution due to correlated neutrons is visible.« less
Authors:
 [1] ; ORCiD logo [1]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Report Number(s):
LLNL-PROC-720437
Journal ID: ISSN 0018-9499
Grant/Contract Number:
AC52-07NA27344
Type:
Accepted Manuscript
Journal Name:
IEEE Transactions on Nuclear Science
Additional Journal Information:
Journal Volume: 64; Journal Issue: 7; Conference: SORMA West, Berkeley, CA (United States), 23-26 May 2016; Journal ID: ISSN 0018-9499
Publisher:
IEEE
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
22 GENERAL STUDIES OF NUCLEAR REACTORS; correlated neutrons; fast neutron counting; scintillator detectors
OSTI Identifier:
1343820

Chapline, George F., and Verbeke, Jerome M.. Characterization of Fissile Assemblies Using Low-Efficiency Detection Systems. United States: N. p., Web. doi:10.1109/TNS.2017.2663379.
Chapline, George F., & Verbeke, Jerome M.. Characterization of Fissile Assemblies Using Low-Efficiency Detection Systems. United States. doi:10.1109/TNS.2017.2663379.
Chapline, George F., and Verbeke, Jerome M.. 2017. "Characterization of Fissile Assemblies Using Low-Efficiency Detection Systems". United States. doi:10.1109/TNS.2017.2663379. https://www.osti.gov/servlets/purl/1343820.
@article{osti_1343820,
title = {Characterization of Fissile Assemblies Using Low-Efficiency Detection Systems},
author = {Chapline, George F. and Verbeke, Jerome M.},
abstractNote = {Here, we have investigated the possibility that the amount, chemical form, multiplication, and shape of the fissile material in an assembly can be passively assayed using scintillator detection systems by only measuring the fast neutron pulse height distribution and distribution of time intervals Δt between fast neutrons. We have previously demonstrated that the alpha-ratio can be obtained from the observed pulse height distribution for fast neutrons. In this paper we report that we report that when the distribution of time intervals is plotted as a function of logΔt, the position of the correlated neutron peak is nearly independent of detector efficiency and determines the internal relaxation rate for fast neutrons. If this information is combined with knowledge of the alpha-ratio, then the position of the minimum between the correlated and uncorrelated peaks can be used to rapidly estimate the mass, multiplication, and shape of fissile material. This method does not require a priori knowledge of either the efficiency for neutron detection or the alpha-ratio. Although our method neglects 3-neutron correlations, we have used previously obtained experimental data for metallic and oxide forms of Pu to demonstrate that our method yields good estimates for multiplications as large as 2, and that the only constraint on detector efficiency/observation time is that a peak in the interval time distribution due to correlated neutrons is visible.},
doi = {10.1109/TNS.2017.2663379},
journal = {IEEE Transactions on Nuclear Science},
number = 7,
volume = 64,
place = {United States},
year = {2017},
month = {2}
}