morgan burks, llnllux.physics.ucdavis.edu/nssc_summerschool/lib/exe/fetch... · 2012. 6. 30. ·...
TRANSCRIPT
Q1135-PPT# author LLNL-PRES-557477 1
Photo: On the way to El Centro Atómico Bariloche, in Patagonia (Argentina) for a reconnaissance trip
Morgan Burks, LLNL
Q1135-PPT# author LLNL-PRES-557477
Scientific • Sun: solar flares • Galactic objects: pulsars, supernova remnants, molecular
clouds, hard x-ray sources • Extra Galactic objects: quasars, galactic centers, gamma-ray
bursts
Medical • Positron Emission Tomography (PET)
— Radioactive tracer emitting positrons — Each 511 keV photon detected by scintillator detector in coincidence
• Gamma Camera (Anger Camera): — hot thallium-201 or technetium-99m source — NaI detector with collimator and position sensitive PMT’s
National Security • Counter terrorism: finding/locating radioactive materials • International Safeguards: verifying facility operation • Treaty verification/ Arms control: imaging and/or counting
warheads
2
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CGRO flew from 1991 to 2000
Designed for gamma-rays from 20 keV to 30 GeV
The Compton telescope consisted of two detector arrays.
• upper array: NE 213A liquid scintillator
• lower array: NaI crystals.
1 to 3 MeV gamma ray map from the
Compton Telescope on board CGRO)
Crab Nebula
Q1135-PPT# author LLNL-PRES-557477
• In Earth orbit since Feb. 2002
• Images gamma-rays from 3 keV to 20 MeV
• Images Sun to understand particle acceleration and energy release in solar flares.
• Consists of 9 Ge coax detectors
• Uses rotating modulation collimators to form the image
RHESSI Ramaty High Energy Spectroscopic Solar Imager
Q1135-PPT# author LLNL-PRES-557477
Fourier-transform imaging
9 rotating modulation collimators (grid pairs)
Field of View:
Full Sun (~1 degree)
Angular Resolution
2 arcseconds to 100 keV 7 arcseconds to 400 keV 36 arcseconds above 1 MeV Source sizes that can be imaged ~2 arcseconds to ~180 arcseconds Instrument Non-position sensitive Ge detector Complex collimator required
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• Used in nuclear medicine to measure metabolic activity in terms of regional glucose uptake
• Uses radioactive tracer that emits positrons
• Positrons annihilate locally and give off two back to back 511 keV photons
• The photon are detected in coincidence
• Image reconstruction techniques are used to form a 3D picture of the region of interest
• Often used in conjunction with a CT scan
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• Uses radio tracers such as thallium-201 or technecium-99m
• Gamma-rays are detected by an array of scintillators / PMT’s.
• A multi-hole collimator limits the field of view to a small window
• The system is then scanned across the region of interest
• High resolution can be achieved at the price of high dose
Q1135-PPT# author LLNL-PRES-557477
Low energy
• <300 keV
• Photoelectric effect dominant
• collimator based imaging
• Coded aperture
• RMC
• Fourier Transform imagers
• variations
Medium energy
• 300 keV to 10 MeV
• Compton effect dominates
• Compton imaging
High energy
• > 10 MeV
• Pair production dominates
• Pair telescopes
Germanium
Q1135-PPT# author LLNL-PRES-557477
1
2
011cosEEE
cmE
The Compton scattering formula gives :
4321 EEEEE
r1
r2
r3
r4
1E
E
12r
source 1. Measurement: The position and
energy of each gamma-ray interaction
must be measured.
2. Tracking: The order of interactions
must be determined using various
physical constraints
3. Compton reconstruction: The initial
scatter angle is then determined by
the Compton formula
4. Image reconstruction: The image is
then built event by event
Q1135-PPT# author LLNL-PRES-557477
image1
)cos1(12
0
'
cm
E
EE
Germanium-Based Compton Imager
Arthur H. Compton
1. ray interacts at multiple locations in the detector. Measure position and energy of each interaction.
2. Scatter angle given by Compton Scatter equation
3. Each -ray resolves to a ring on the sky map.
image1
4. Many -rays form an image
Measured point source 1408 keV (152Eu) Resolution ~1.20
longitude
lati
tud
e
longitude
lati
tud
e
x1
-+
-+
x2
y2
y1
++
- -
x1
-+
-+
x2
y2
y1
++
- -
image5
image5
image5
~0 deg (on-axis)
30 deg
60 deg
image5
N0
359
i 0
179
j
image2i j
0
359
i 0
179
j
image1i j
image5
45 deg
N0
359
i 0
179
j
image2i j
0
359
i 0
179
j
image1i j
image5
75 deg
60 deg (in 3-D for comparison)
Q1135-PPT# author LLNL-PRES-557477
image1
image1
image1
image1 image1
1408 keV(0 deg to 60 deg)
600
450
300
150
00
• Eu152 source was used to measure the point spread function vs. energy and angle
• Excellent angular resolution was achieved across broad energy range.
0 300 600 900 1200 15000
0.25
0.5
0.75
1
1.25
1.5
Energy (keV)
Imag
ing R
eso
lutio
n (
deg
rees)
ARM vs. Energy (at 30 degrees)
Measured
Simulated
ARM (Angular Resolution Metric) = Full-Width Half-Power (fwhp)
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Q1135-PPT# author LLNL-PRES-557477
0 200 400 600 800 1000 1200 14000
100
200
300
400
500
Energy Spectrum
1274
keV
511 keV
00
22Na
22Na
137Cs
image2
662
keV?
360o Compton imager
looking at various
sources
sumimage
Image: 511 keV
Image: 662 keV (shown in 3-D)
Resulting spectrum
Q1135-PPT# author LLNL-PRES-557477
5 10 15 20 25 30 35
5
10
15
20
25
30
35
col
row
0 1250 2500 3750 5000 6250 7500
first_pt_source_no_back
Simulated Ideal Imaging Response
1. Mask pattern and
position sensitive
detector
2. Detector after point
source exposure
3. De-convolved point
source image
Coded Aperture Imagers
• Good for point sources
• Not effective for extended sources
• Best for gammas rays < 300 keV
• Requires position sensitive detector
• Limited Field of View
Q1135-PPT# author LLNL-PRES-557477
The gamma-ray imaging spectrometer uses a coded aperture and a multi-element position-sensitive detector
Gamma-ray camera imaging
the Peacekeeper missile
Gamma-ray image of
Peacekeeper missile
clearly shows ten
warheads
Q1135-PPT# author LLNL-PRES-557477
PFEP (Pilot Fuel Enrichment Plant) Natanz, Iran
Research funded by the DOE Office of Nonproliferation and International Security (NA-24)
Collaboration includes • Euratom: European Atomic Energy Community • ABACC: Brazilian-Argentine Agency for Accounting and Control of Nuclear Materials • Oakridge National Laboratory • Lawrence Livermore National Laboratory • Lawrence Berkeley National Laboratory Purpose • To demonstrate a use for gamma-ray imaging in International Safeguards applications Applications include • Design Information Verification (DIV) • Materials accountancy • “Hold-up” location and quantification • Decontamination and Decommission
Q1135-PPT# author LLNL-PRES-557477
Dual Planar Compton Imager
Power Controller
Electronic Readout
Imager
Laptop for imaging and analysis
Design: dual ―thin‖ germanium planar detectors with 3 mm voxels
Readout: Custom 32-channel digitizer; USB to Laptop
Multiplexing: In progress (5 to 1 multiplexing demonstrated, trying for higher ratio)
Spectral resolution: 1.8 keV
Angular resolution: 7o (target = 3.5o)
Power Consumption: 15 watts (plus laptop power)
Cooling: Prototype uses liquid nitrogen. Next generation will be mechanically cooled
Cost: $150k
Imaging system designed and built in collaboration with PHDs Co., Knoxville TN
Q1135-PPT# author LLNL-PRES-557477
Gamma-ray imaging is greatly aided by addition of 3D LIDAR
Zoller + Froehlich 5006 laser scanner
Resolution: 1 to 7 mm
Range: up to 79 meters
Data rate: 1 Megapixels / second
FOV: 360o horizontal 310o vertical
Scan time: few minutes
Q1135-PPT# author LLNL-PRES-557477
A 2D gamma-ray image is backprojected onto the range
map – snapshot of the 3D model - top view
A 2D gamma-ray image is backprojected onto the range
map – snapshot of the 3D model - side view;
3D Backprojected image: 3000 total number of photons; 3 CCI
positions; 31000 voxel elements; 5x5x5cm3 voxel size
3D Reconstructed image: 3000 total number of photons; 3 CCI
positions; 31000 voxel elements; 5x5x5cm3 voxel size
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• Process Buildings: 1100 x 970 feet
• # enrichment stages: 1760
• Peak Power Consumption: >2 GW
• # of control instruments: 85,000
• Miles of Process Piping: ~400
• Only uranium diffusion plant in U.S.
• In operation since 1952
• Began by making feedstock for weapons
• Now makes LEU for commercial power
Q1135-PPT# author LLNL-PRES-557477
Buildup in restricted pipe • Many pipes hidden behind heat shielding. However, they can still be
measured and the contamination located with the gamma-ray imager
Transfer / Withdrawal stations • Where product is transferred from to and from containers for
shipment: This is an obvious place where one would want to monitor the process
Gas flow through pipes • Measuring absolute enrichment is hard with gamma-ray spectroscopy
(or imaging) alone. It is also necessary to know the gas density. However, relative enrichment can be measured (or change detection).
Contaminated equipment • Monitor equipment for storage or decontamination and
decommission.
24
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Purpose of measurement campaign:
1. Test instrumentation in a real-world environment
2. Demonstrate relevance to International Safeguards applications
Challenges 1. Extremely hot (>115 oF) 2. Restricted spaces and physical
barriers 3. Limited facilities (electrical, LN2
etc.) 4. Dust 5. Radioactive contamination 6. Significant access restrictions
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Imaging known neptunium deposit
3D-LIDAR
Compton Imager Coded Aperture Imager
3D LIDAR makes 360 degree laser image of the room Coded aperture has 45 degree field of view and must be aimed in the right direction Compton imager has 4-pi field of view
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Measured Spectrum
(enriched uranium flow pipe w/ contamination)
0 100 200 300 400 500 600 700 800 900 10001
10
100
1 103
1 104
Energy (keV)
5500
1
h1i
105000 i
300, 312, 340, 398, 415 keV
237Np(233Pa)
1001 keV
238U(234mPa)
186keV 235U
Q1135-PPT# author LLNL-PRES-557477
Compton imager localized “hot spot” and identified it as Np-237
29
0 200 400 600 800 1000 120010
100
1 103
1 104
Energy (keV)
Spectrum from Contaminated pipe
Gamma-Spectroscopy (and imaging)
location of contaminated piping
186keV 235U
766, 1001 keV
238U(234mPa)
Spectroscopy clearly identifies contamination of U-235 and U-238. Gamma image not shown due to proprietary design concerns on piping; however, image was easily able to localize contamination
30
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Coded Aperture Image of low enriched UF6
flowing through process pipe (Klaus Ziock et. al, ORNL)
Image based on 186 keV lines from U-235
Acquisition time: ~ hour
fiducial markers allow alignment of visual, LIDAR and gamma image
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311 keV distribution
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Q1135-PPT# author LLNL-PRES-557477
First field demonstration of a Compton-based gamma-ray imager
• Demonstrated ease of portability/use in a real-world environment
• Prototype efficiency was low but still took valuable measurements
Next steps: looking at arms control applications (NA-22 funding)
• Building an upgraded instrument
— Increased sensitivity
— Increased portability
— Mechanical cooling
— Built in panoramic camera
34
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC
Q1135-PPT# author LLNL-PRES-557477
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Q1135-PPT# author LLNL-PRES-557477
1. Gamma-ray imaging is a powerful tool for locating and identifying radioactive materials
2. This technology is advancing quickly
3. Has potential application to Safeguards problems such as DIV
4. NA-24 funded international collaboration
5. A combination of measurements and measurements were used
Process test bench for reprocessing study in the Nuclear Fuel Cycle Safety Engineering Research Facility (NUCEF) -JAEA
Q1135-PPT# author LLNL-PRES-557477
Coded Aperture
Range: ~100 meters
1-D and 2-D imaging
Modest field of view (45o)
Have built 16 cm2 to 8000 cm2 systems
Typically <300 keV
Point sources
Rotation Modulation Collimators
Range: 92 million miles!
Requires lots of signal!
No terrestrial systems deployed (to my knowledge)
Narrow FOV
Up to 1 MeV
x
z
y
Compton
Range: 10’s of meters
2-D, 3-D & 4- imaging
Up to 1.4 MeV
High imaging resolution
Extended and point sources
Q1135-PPT# author LLNL-PRES-557477
Q1135-PPT# author LLNL-PRES-557477
1. Locate source
2. Image source: Differentiate extended vs point-like sources
3. Differentiate complex mixed sources
4. Increased sensitivity: separate signal from background
1x10 1
1x10 2
1x10 3
1x10 4
1x10 5
0 500 1000 1500 2000 2500 3000
Co
un
ts
Energy (keV)
High-resolution spectrum of typical background
radiation
• Natural uranium (granite,
pottery) and depleted uranium
(ammunition, counterweights) are
common
• Both 232U, present in most but
not all HEU, and background 232Th decay to 208Tl emit gamma
rays at 2615 keV
• Medical isotopes can walk
around!
Background varies with
location and time
Compact Compton
Imager CCI-2
Compact Compton
Imager CCI-1
•Improvements in :
–Sensitivity (x10 increase, as
compared with CCI-1)
–Count rate capability (x100
increase, as compared with CCI-
1, now 10kHz)
–Real-time imaging capability
demonstrated recently.
•1 Ge plus 1 Si DSSD detectors in two
cryostats/ 1st generation DAQ/ cart
•Highlights:
–2D Gamma-ray imaging
–Demonstration of spectroscopy
from a limited spatial area
–Demonstration of stand-off 3D
imaging
–Demonstration of near-field 3D
imaging
•2 Ge +2 Si DSSD detectors in two cryostats/ 2nd generation DAQ/ no
cart