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Title: Neutron spectrometer for improved SNM search.

Abstract

With the exception of large laboratory devices with very low sensitivities, a neutron spectrometer have not been built for fission neutrons such as those emitted by special nuclear materials (SNM). The goal of this work was to use a technique known as Capture Gated Neutron Spectrometry to develop a solid-state device with this functionality. This required modifications to trans-stilbene, a known solid-state scintillator. To provide a neutron capture signal we added lithium to this material. This unique triggering signal allowed identification of neutrons that lose all of their energy in the detector, eliminating uncertainties that arise due to partial energy depositions. We successfully implemented a capture gated neutron spectrometer and were able to distinguish an SNM like fission spectrum from a spectrum stemming from a benign neutron source.

Authors:
;
Publication Date:
Research Org.:
Sandia National Laboratories
Sponsoring Org.:
USDOE
OSTI Identifier:
908879
Report Number(s):
SAND2007-1570
TRN: US0703788
DOE Contract Number:
AC04-94AL85000
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 73 NUCLEAR PHYSICS AND RADIATION PHYSICS; CAPTURE; FISSION; FISSION NEUTRONS; LITHIUM; MODIFICATIONS; NEUTRON REACTIONS; NEUTRON SOURCES; NEUTRON SPECTROMETERS; NEUTRON SPECTROSCOPY; NEUTRONS; Nuclear materials-Monitoring.; Nuclear reactors-Materials.; Nuclear power plants-Materials.; Nuclear spectroscopy.

Citation Formats

Vance, Andrew L., and Aigeldinger, Georg. Neutron spectrometer for improved SNM search.. United States: N. p., 2007. Web. doi:10.2172/908879.
Vance, Andrew L., & Aigeldinger, Georg. Neutron spectrometer for improved SNM search.. United States. doi:10.2172/908879.
Vance, Andrew L., and Aigeldinger, Georg. Thu . "Neutron spectrometer for improved SNM search.". United States. doi:10.2172/908879. https://www.osti.gov/servlets/purl/908879.
@article{osti_908879,
title = {Neutron spectrometer for improved SNM search.},
author = {Vance, Andrew L. and Aigeldinger, Georg},
abstractNote = {With the exception of large laboratory devices with very low sensitivities, a neutron spectrometer have not been built for fission neutrons such as those emitted by special nuclear materials (SNM). The goal of this work was to use a technique known as Capture Gated Neutron Spectrometry to develop a solid-state device with this functionality. This required modifications to trans-stilbene, a known solid-state scintillator. To provide a neutron capture signal we added lithium to this material. This unique triggering signal allowed identification of neutrons that lose all of their energy in the detector, eliminating uncertainties that arise due to partial energy depositions. We successfully implemented a capture gated neutron spectrometer and were able to distinguish an SNM like fission spectrum from a spectrum stemming from a benign neutron source.},
doi = {10.2172/908879},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Mar 01 00:00:00 EST 2007},
month = {Thu Mar 01 00:00:00 EST 2007}
}

Technical Report:

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  • A neutron spectrometer utilizing a lithium-containing scintillator is proposed. The proposal is based on the ability to distinguish the (n, alpha ) reaction from other events by pulse-shape analysis. The ability to distinguish neutron events from gamma-ray events in stilbene by pulse-shape techniques was demonstrated experimentelly. A pulseshape effect was looked for in a commercial Li/sup 6/I(Eu) scintillator without success. The literature was searched for other lithium-containing phosphors which might show the effect. (auth)
  • Progress on instrument development at LLL is described. Projects covered include: improved electronics configuration for LLL neutron spectrometer system; development of a high resolution neutron spectrometer for field use; modified chlorine and hydrogen chloride cartridge testing system; and a portable gamma spectrometer. (GHT)
  • An innovative helium3 high pressure gas detection system, made possible by utilizing Sandia's expertise in Micro-electrical Mechanical fluidic systems, is proposed which appears to have many beneficial performance characteristics with regards to making these neutron measurements in the high bremsstrahlung and electrical noise environments found in High Energy Density Physics experiments and especially on the very high noise environment generated on the fast pulsed power experiments performed here at Sandia. This same system may dramatically improve active WMD and contraband detection as well when employed with ultrafast (10-50 ns) pulsed neutron sources.
  • A program of simulations and validating experiments was utilized to evaluate a concept for neutron interrogation of commercial cargo containers that would reliably detect special nuclear material (SNM). The goals were to develop an interrogation system capable of detecting a 5 kg solid sphere of high-enriched uranium (HEU) even when deeply embedded in commercial cargo. Performance goals included a minimum detection probability, P{sub d} {ge} 95%, a maximum occurrence of false positive indications, P{sub fA} {le} 0.001, and maximum scan duration of t {le} 1 min. The conditions necessary to meet these goals were demonstrated in experimental measurements even whenmore » the SNM is deeply buried in any commercial cargo, and are projected to be met successfully in the most challenging cases of steel or hydrocarbons at areal density {rho}L {le} 150 g/cm{sup 2}. Optimal performance was obtained with a collimated ({Delta}{Theta} = {+-} 15{sup o}) neutron beam at energy E{sub n} = 7 MeV produced by the D(d,n) reaction with the deuteron energy E{sub d} = 4 MeV. Two fission product signatures are utilized to uniquely identify SNM, including delayed neutrons detected in a large array of polyethylene moderated 3He proportional counters and high energy {beta}-delayed fission product {gamma}-radiation detected in a large array of 61 x 61 x 25 cm{sup 3} plastic scintillators. The latter detectors are nearly blind to normal terrestrial background radiation by setting an energy threshold on the detection at E{sub min} {ge} 3 MeV. Detection goals were attained with a low beam current (I{sub d} = 15-65 {micro}A) source up to {rho}L = 75 g/cm{sup 2} utilizing long irradiations, T = 30 sec, and long counting times, t = 30-100 sec. Projecting to a higher beam current, I{sub d} {ge} 600 {micro}A and larger detector array the detection and false alarm goals would be attained even with intervening cargo overburden as large as {rho}L {le} 150 g/cm{sup 2}. The latter cargo thickness corresponds to 8 ft of hydrogenous or metallic cargo at the highest density allowed by the weight limit of the container. Simulations support the efficacy of this technique in the most challenging cases and experimental measurements are shown validating these predictions. Signal and background levels have been assessed and utilized to predict error rates due to false positive and false negative results. The laboratory system demonstrates the ability to detect HEU in amounts as small as m {ge} 250 g buried in the middle of a maximum density cargo and to do so with error rates that meet the goals given above. Higher beam current allows reliable SNM detection in shorter irradiation and/or counting times and with more challenging cargo threat scenarios.« less