Lawrence Livermore National Laboratory
New and Novel Nondestructive Neutron and Gamma-Ray Technologies Applied to
Safeguards
Arden D. Dougan, Neal Snyderman, Les Nakae, Dan Dietrich, Phil Kerr, Tzu-Fang Wang, Wolfgang Stoeffl, Stephan Friedrich, Lucian Mihailescu
Presented to the JAEA-IAEA Workshop on Advanced Safeguards Technology for the Future Nuclear Fuel Cycle
This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 UCRL-PRES-235638
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Novel Science and Technology Solutions for Safeguards
Compact Compton imager combined with 3D LIDAR for Design
Information Verification
Superconducting gamma-ray
spectrometer for ultra-precise sample
analysis
New Correlated Fast Neutron Counting
technique using Liquid Scintillator Multiplicity
counter and nanosecond timing
Next generation high efficiency neutron
detectors based on pillar technology
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Superconducting γ-Ray Spectrometer (Ultra-Spec)
Si3N4
NbAl
Mo
Si Substrate
Mo/Cu thermistor
Sn absorber (0.25mm3)
γ-ray
Energy resolution ΔEFWHM = 2.355 k BT2CSource
Cold fingerwith detector
Refrigerator
Temperaturecontrol
Electronicread-out
HPGe
UltraSpec
90 92 94 96 980
50
100
150
200
250
300
350
Cou
nts
Energy [keV]
Pa Kα1 Pa K
α2
U Kα1
U Kα2
Th Kα1
(↔235U)
234Th (↔238U)
Gamma-ray absorption increases absorber temperature, which is measured with a superconductingthermometer
Low-temperature operationenables ultra-high energy resolution, <80 eV FWHM.
Operating Principle Spectrometer
Results
ApplicationsUltra-high energy resolution greatlyincreases precision of isotope ratio measurements in cases where HPGedetectors are affected by line-overlap.
e.g. MGA for Pu at 100keV, MGA-U for U at 92keV2006
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We are developing a compact Compton imager
The Compton camera determines the direction of the gamma ray by tracking its interactions inside a multilayered detector system.Compton imaging provides 180 deg field of view, 2 deg angular resolution (3 cm at 1 m), 2 keV energy resolution, and can image the 186 keV 235U line and the 375 and 414 keV 239Pu lines. It takes 5 min to image 1 g 239Pu in a 6 cm pixel, 2 m away
We have built and tested the first Compton camera to take advantage of the new semiconductor strip detector technology that enables high-spatial-resolution, collimatorless imaging.
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Verification of material hold-up and diversion in enrichment plants by combining 3D laser ranging with Compton camera gamma-ray imaging
Combining wide field-of-view gamma-ray imagers with 3D range maps obtained with a Design Information Verification (DIV) lidarscanner improves the fidelity of the gamma-ray image and adds a capability to directly measure isotope hold-up information compared to using laser ranging alone.
Lidar scans will provide the map of objects in the environment. The Compton camera measures the gamma-ray image.
Monte Carlo simulation of the gamma-ray intensity image of Pu-239 hold-up in a pipe elbow.
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Measurements demonstrate gamma-ray imaging of materials in pipes
Reconstructed gamma-ray image measurements of a Eu-152 344 keV gamma-ray line source (analog for the Pu-241 414 keV line) hidden in a pipe are shown as contour plots on top of visual panoramic images of the Lab.
Expectation-Maximization Maximum Likelihood (EM-ML) Algorithm
Compton imaging will help inspectors verify plant designs, design changes, diversion of SNM, movement of SNM, hold-up and material accumulation.
Raw Compton image Filtered Back-projections using Spherical Harmonics
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Mapping of gamma-ray images onto 3D range maps – side view
A gamma-ray image is back-projected onto the range map – snapshot of the 3D model (side view)
Virtual Scan axis
Gamma-ray imaging axis
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New method: Correlated Fast Neutron Counting
Fast neutron counting enables isolation of individual fission events This will enhance the capability to statistically determine the fission isotopes in a mixed TRU stream—Cm versus Pu
With 60 keV active interrogation, we can preferentially fission 239Pu (and 235U) over 242Cm—239Pu and 240Pu dominate in concentration and
fission cross section
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Measured Count Distributions
Random Source (AmBe) 2.1K cts/sec
Fission Source
S.F., M=1, eff ~ 3%252 Cf 3.1K cts/sec
06122002_143810-2A, Gate 512, 512 usecs
Tim
es p
er 1
0^6
cycl
es
Number of counts per cycle
100
101
102
103
104
105
106
107
-1.000 1.000 3.000 5.000 7.000 9.000 11.000
datapoisson
06132002_104441-2A, Gate 512, 512 usecs
Tim
es p
er 1
.3 x
10^
8 C
ycle
s
Number of counts per cycle
10-1
100
101
102
103
104
105
106
107
108
-1.000 2.000 5.000 8.000 11.000 14.000
datapoisson
Correlated Fission Source has wider distribution than predicted from Poisson (Random) with the same count rate
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Individual Fission Chain Detection
Time Since Start of Burst (s)
Fission chain burst is easily distinguished from cosmic ray background
Measured data from 22 kg bare HEU shell
Neu
tron
Num
ber
Sin
ce F
irst i
n B
urst
Δt I
nter
val
Bet
wee
n C
ount
s
1 μs
100 μs
10 ms
1 s
10 ns
0
10
20
40
0 0.1 0.2 0.3 0.4 0.5
30
+ n Detector• Cosmic Ray Detector
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0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0 1 2 3 4 5 6 7 8
Induced Fission Neutron Distributions
U235 inducedPu239 induced
Pro
babl
ility
per F
issi
on
Number of Neutrons per Fission
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0 1 2 3 4 5 6 7 8
Spontaneous Fission Neutron Distributions
Pu240 sponCf252 spon
Pro
babi
lity
per F
issi
on
Number of Neutrons per Fission
• SNM fissions with an expectation of 2-4 neutrons• Finite probability of more (especially with multiplication)
Fission Neutron Distributions
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Time Scales: What does timing buy?
10-9
(ns)10-6
(μs)10-3
(ms)
Time (s)
Individual Fission
Fission Chains (metal)
Neutron Thermalization Time(3He/10B detectors, reactors)
Liquid Scintillator/Stilbene Detection Time
Liquid Scintillator is fast (nanoseconds) can detect individual fissions even in high count rate environments
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High source count rate requires new technologies
With our new Liquid Scintillator array and nanosecond timing data acquisition
We have demonstrated isolation of fission chains in Pu
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Discrimination of neutrons and gamma-rays with liquid scintillator
105 discrimination of neutrons and gamma-rays above 500 keV neutron energy
Neutrons
Tail
Rat
io
2” lead between 252Cf and stillbenedetector
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• Use low-energy neutrons to induce fission in 235U and 239Pu
• Detect fission neutrons— Liquid Scintillator detectors— Pulse-shape discrimination— High-energy neutrons— Low background
Proof-of-ConceptSystem
Diagram
Active interrogation
60 keV neutrons preferentially fission 235U and 239Pu over 242CmThe fission cross section for 238U is even smaller
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60-keV neutron interrogation
Induce fission in Pu— Detect high-energy fission neutrons
with Liquid Scintillator Detectors— Pulse-shape discrimination separates
fission neutrons and gamma rays− Energy Threshold detectors− Neutron beam energy well below
detector energy threshold
Low-energy neutron interrogation provides a rapid signature for the
presence of 235U
Single 3”x3” Detector
Single 3”x3” Detector
60-keV neutrons from proton beam
RFQ: 7Li(p,n)
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Low Energy Neutron Interrogation with fast scintillator detection
Only SNM Pu, 235U readily fission from low energy neutronsMeasuring with fast scintillator preserves neutron energy Detector can be made invisible to interrogation BeamChanges in Fast Neutron Signature can help distinguish Neutron Source (e.g. Cm from Pu, HEU from LEU or DU) Fast Neutron Detection allows Pulsed Interrogation with Portable D-D or D-T generators.
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Solid-state neutron detectors
LiF, 10B solid state neutron detectionUbiquitous neutron detectionLow power consumptionInsensitive to gammasPreamplification for each detector, signals can be transmitted via wire or wirelessPreamplifier performs as well as commercial unit 14%
15%
LLNL preamp Commercial preamp
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Nanotechnology can lead to dramatic improvements in radiation detection
3D matrix of semiconductor nano-crystals
• Tuning the size of the nano-crystals will allow optimal scintillator-photodetector match.
3D semiconductor pillars surrounded by a boron-10 matrix
• Tuning the size of the pillars will lead to improved efficiency.
For neutron detection
For gamma-ray detection
The ability to control semiconductor dimensions at the nano/micro-scale can potentially lead to the next generation radiation detectors.
The ability to control semiconductor dimensions at the nano/micro-scale can potentially lead to the next generation radiation detectors.
Radiation Scintillation
Radiation electrons/holescollected
20Option:UCRL# Option:Additional Information
Lawrence Livermore National Laboratory
Pillar device for high efficiency neutron detection
Simulations indicate this 3-D structure will increase efficiency towards 85+% / cm2 !
Device geometry: etch depth → capture neutron
fluxpitch → alpha particle range
Simulations indicate this 3-D structure will increase efficiency towards 85+% / cm2 !
Device geometry: etch depth → capture neutron
fluxpitch → alpha particle range
10B efficiently produces α particles
But….Most α particles do not reach the detector!Limited efficiency: 2-5%/cm2 (@ thermal)
10B efficiently produces α particles
But….Most α particles do not reach the detector!Limited efficiency: 2-5%/cm2 (@ thermal)
10B+n → 7Li(0.84MeV) + α(1.47MeV)(Q=2.31MeV, σ=3571b)
10B+n → 7Li(1.01MeV) + α(1.78MeV)(Q=2.79MeV, σ=269b)
94 %
6%
Z1RR
A
B Z2
+, -Electron-hole pairsD
etec
tor
C
onve
rter
Neutrons
Charged particles(α, 7Li)10Boron
+
-
Etch
ed d
epth
Neutrons
Si
10B
+, -Electron-hole pairs
Charged particles(α, 7Li)
Planar 2D Design LLNL Pillar 3D Design
pitch
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Next generation high efficiency detectors based on pillar technology
Neutron detection efficiency can be as high as 50%Can be filled with 10B, LiF or threshold fission materials
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Applications for solid-state neutron detectors
“Smart tags” for tracking material flowMonitor centrifuge hallStorage area, transport through pipes, etc.Ubiquitous detection
Next steps: Need to do simulations and measurements to demonstrate this capability for specific Safeguards regimes