morgan burks, llnllux.physics.ucdavis.edu/nssc_summerschool/lib/exe/fetch... · 2012. 6. 30. ·...

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


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


• 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


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

http://hesperia.gsfc.nasa.gov/hessi/images/Angular_Coverage.jpg


• 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


• 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


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


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


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)


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)


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


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


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


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


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


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


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


• 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


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


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

Q1135-PPT# author LLNL-PRES-557477 26 26

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


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


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


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


311 keV distribution


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


35


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


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


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

morgan burks, llnllux.physics.ucdavis.edu/nssc_summerschool/lib/exe/fetch... · 2012. 6. 30. ·...

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