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O. Kamaev, V. Anghel, A. Erlandson, C. Jewett, S. Livingstone,E. Rand, M. Thompson, B. van der Ende
Canadian Nuclear Laboratories
International Workshop on Numerical Modelling of Non-Destructive Assay Instrumentation and Methods for Nuclear Safeguards
16 – 17 May 2018
Integrated System Based on Muon
Tomography for Nuclear Security and
Safeguards
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Challenges in Nuclear Security and SafeguardsObjectives of IAEA safeguards: “the timely detection of diversion of significant quantities of nuclear material from peaceful nuclear activities to the manufacture of nuclear weapons … and deterrence of such diversion by the risk of early detection”.
IAEA Safeguards Glossary
• Prevent or deter the theft of special nuclear material (SNM), detect illicit movement: facility / border security
• Characterise legacy nuclear waste stored within industrial containers: waste management verification / non-proliferation
Detection of shielded illicit radioactive materials, including SNM, is a long standing challenge.
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Muon Tomography for Nuclear Safety & Security
Muon Scattering Tomography (MST) technique:
• Muons are highly penetrating and are hard to shield.• Employs the multiple Coulomb scattering of naturally
occurring cosmic-ray muons inside a material.• Allows a passive non-destructive assay of large-volume
objects.• Detects the presence of high-density / high-Z materials.
scattering
angle q
muon
material
Integrated System for detecting radioactive materials:
Motivation? To increase the accuracy and speed of detecting shielded SNM.How? By integrating muon tomography with gamma-ray, neutron detectors:
• Experimental tests with multiple technologies towards integration.• Monte Carlo simulations for lab-scale systems.
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Multiple Passive Technologies for SNM DetectionMuon tomography:Is there illicit high-density object?Where is it exactly inside a container?
High resolution gamma spectroscopy:Is radioactive/nuclear material present?What is the source?
Neutron counting:Is it SNM?What is the mass?
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Muon Tomography DetectorCosmic Ray Inspection and Passive Tomography (CRIPT) – a scintillator-based MST detector at Canadian Nuclear Laboratories.
UV and blue light is produced by muon’s interactions in scintillators
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Muon Tomography DetectorCosmic Ray Inspection and Passive Tomography (CRIPT) – a scintillator-based MST detector at Canadian Nuclear Laboratories.
Position-sensitive super-layer
UV and blue light is produced by muon’s interactions in scintillators
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Muon Tomography DetectorCosmic Ray Inspection and Passive Tomography (CRIPT) – a scintillator-based MST detector at Canadian Nuclear Laboratories.
121 x and 121 y bars per super-layer2.0 m x 2.0 m in area
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CRIPT Muon Tomography Detector
Deflection in
high-Z target
Target
area
Muon
Spectrometer for
muon momentum
Detector
Layers
5.3 m tall
“A plastic scintillator-based muon tomography system with an integrated muon spectrometer”, Nuclear Instruments and Methods in Physics Research A 798 (2015)
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CRIPT Detector: Output
2 hours of data5 cm voxels8 hit threshold
with high-density Pb flaskw/o flask
Images:• Collect enough data in enough voxels and
create an image (we get ~60 muons/s).• Sophisticated image reconstruction algorithm
(Canada Patent 2838656, 2012).• A qualitative result, rather than a quantitative.
Detection parameter:• Evaluated with Geant4 Monte Carlo studies.• Selected parameter: median logarithm of the
scattering density estimate (SDE).
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CRIPT Detector: Output
2 hours of data5 cm voxels8 hit threshold
with high-density Pb flaskw/o flask
Images:• Collect enough data in enough voxels and
create an image (we get ~60 muons/s).• Sophisticated image reconstruction algorithm
(Canada Patent 2838656, 2012).• A qualitative result, rather than a quantitative.
Detection parameter:• Evaluated with Geant4 Monte Carlo studies.• Selected parameter: median logarithm of the
scattering density estimate (SDE).• High-density/Z material produces the tail on
the right side of the distribution.
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Gamma-ray DetectorWith light or irregular shielding, gamma-rays are easy to detect.High-purity germanium (HPGe) detector:• Relative efficiency: 25% @ 1.3 MeV• Energy resolution: FWHM 1.8 keV @ 1.3 MeV• Endcap diameter: 76 mmUtilized γ-lines from Uranium:• 238U via 234mPa: 1001, 766, 258 [keV].• 235U: 186 keV.
Energy [keV] Time [days]
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Neutron DetectorNeutrons are fairly unique to SNM.Boron-lined hybrid 10B/3He (B10+) detector:• A boron-lined neutron detector boosted
with 0.75 atm of 3He.• Detector area: ~ 100 x 20 cm2
• Tubes are placed in a high-density polyethylene box. n
• Based on thermal neutron capture by 10B (3840 barn):n + 10B → 7Li*+ α + 2.3 MeV (94%)
→ 7Li + α + 2.8 MeV (6%)• 3He has a large cross-section for capture of thermal neutrons (25 meV):
n + 3He → 3H + p + 0.765 MeV (5400 barn)
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Blind Tests: Typical Setup
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Scenario: Verify that SNM content in storage material is intact.
• Lead flask:
(4.3 cm thick)
Setup: DU inside Lead Flask
Units: inches
10 minutes of data• CRIPT: shows a barrel-like object placed in the center.• HPGe: observed a hint of 238U via 1001 keV γ-line.• B10+: null result consistent with background.
• 55-gallon drum with 2 stacked concrete blocks inside.• High-density polyethylene (HDPE), tungsten rod, fake
metal CANDU fuel bundle, metal objects, sand bags .• Depleted uranium (DU) slugs, ~6 kg in total, were added
during tests – not known to “blind” analysers.
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Setup: DU inside Lead Flask2 hours of data:• HPGe: still observed a hint of 238U.
Estimated min detection time: 10 hours.• CRIPT: observed an anomaly (high-density/Z spot) in horizontal
slices at ~55 cm vertical position.Integral of SDE is 341 ± 18 vs. 319 ± 18 (reference case).
• B10+: clear signal of 22.2 ± 3.0 cpm.Estimated min detection time: 82 minutes.Estimated NU/DU mass: 21.5 ± 4.0 kg.
reference test
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Setup: DU inside Lead Flask
20 hours of data from CRIPT:• Confirmed an anomaly (high-density/Z spot).
Clear difference between “test” and “reference” cases.Reference case: a cavity within high-density material is seen.Test case: cavity is filled with SNM.
reference test
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Setup: LEU inside textile containerScenario: Undeclared, illicit nuclear material inside shipping container with textile.
• Heavy fabric completely filling plywood box.• Low-enriched uranium (LEU) container, 0.5 kg total
weight, was placed into the middle of the box during tests – not known to “blind” analysers.
10 minutes of data• CRIPT: using 4-cm voxels scanning volume appears as
low-density.• HPGe: clear signal of 73.2 ± 0.9 cpm rate for 1001 keV
γ-ray with a background of 5 – 8 cpm.Estimated min detection time: 0.3 minutes.Estimated enrichment: 5.2 ± 1.7 % of 235U.
• B10+: null result with 7.8 ± 10.2 cpm corrected for background.
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Setup: LEU inside textile container2 hours of data• CRIPT: small high-density/Z material was observed
directly in the center.Integral of SDE is 2 vs. 0 (reference case).
• B10+: null result consistent with background. Estimated mass of 235U: 3.7 kg.
20 hours of data from CRIPT
reference test
test
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Integrated Monte Carlo Simulation Framework
• Can include CRIPT, PVT plastic scintillator panels, HPGe, Boron-Coated detectors, 3He tubes.
• Flexible number of gamma-ray, neutron detectors.
• Capable of simulating and detecting coincident signals.
Simulated integrated system based on muon tomography with multiple gamma, neutron detectors
Modular object-oriented framework to support the detection of SNM.• Build upon the Geant4 toolkit
Standard G4 physics lists High-precision neutron physics lists
• Includes FREYA from LLNL Fission Library package for emission of correlated fission secondaries.
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Benchmark/Validation of Integrated Monte Carlo
Experimental setup
Simulation setup
“Small Lead Flask shielding” experiment
Simulated response of PVT panels to neutrons
1H capture
35Cl capture
• Good agreement between experiment PVT measurements with PuBe n-source and simulations.
• Currently assessing performance of the integrated SNM detection system using developed MC simulation framework.
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MC Characterization of 10B/3He Detector
B.M. van der Ende et al., “Use of SRIM and Garfield with Geant4 for the characterization of a hybrid 10B/3He neutron detector”, Nuclear Inst. and Methods in Physics Research, A 894 (2018)
Pulse height spectra from measurement vs. Garfield + SRIM simulation
• Geant4 MC simulation agrees with 252Cf measurements to within 6.4%.
• Extended MC model by simulating raw pulses with Garfield and SRIM.
• Developed tools can be applied to modelling of any gas-based prop. counterfor neutron detection.
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Summary• A passive system based on muon tomography, neutron detection, and gamma-ray
spectrometry for non-destructive assay can address detection of shielded illicit radioactive materials, including SNM, - a long standing challenge. Facility / Border Security Non-proliferation / Waste Management Verification.
• CRIPT, a muon tomography system with unique capability of measuring muon momentum, is in operation at Canadian Nuclear Laboratories.
• Passive neutron and gamma-ray systems were added: Confirm the clear presence of SNM Identify a radioactive source, estimate enrichment Provide an estimate for the mass of SNM.
• Experimental tests with multiple technologies towards integration were performed.• Integrated MC simulation framework was developed and validated - finalizing
performance assessment.
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Backup Slides
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CRIPT Detection Time
60 second scan, 90% success rate with ~1% false alarm rate... But, that is lead in empty container, work continues....
50/50 guess
“A plastic scintillator-based muon tomography system with an integrated muon spectrometer”, Nuclear Instruments and Methods in Physics Research A 798 (2015)