An MPGD Application:An MPGD Application:
Muon Tomography for Muon Tomography for Detection of Nuclear ContrabandDetection of Nuclear Contraband
Marcus Hohlmann,P. Ford, K. Gnanvo, J. Helsby, R. Hoch, D. Mitra
Florida Institute of Technology
2nd meeting of RD51 collaboration, Institute Henri Poincaré, Oct 13, 2008
Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 2
OutlineOutline• Nuclear Contraband
• Muon Tomography– Basic Concept– Existing Work– MPGDs for MT
• Simulation of an MT station– Computing, Generation, Simulation, Reconstruction – Results on Expected Performance
• Plans for R&D on MT Prototypes with MPGDs
Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 3
The Nightmare ScenariosThe Nightmare Scenarios
• Terrorist smuggle highly enriched uranium (HEU) or plutonium across borders and destroy a city by detonating a nuclear bomb, or
• Terrorists smuggle highly radioactive material into a city and disperse it with a conventional explosion (“dirty bomb”) making portions of the city uninhabitable.
T.B. Cochran and M.G. McKinzie, Scientific American, April 2008
Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 4
Challenge in Detecting Nuclear ContrabandChallenge in Detecting Nuclear Contraband
HEU can be hidden from conventional radiation monitoring because emanating radiation is relatively easy to shield within regular cargo
~ 800 Radiation Portal Monitors (n,γ) in U.S.
Scientific American, April 2008
Sci. Am., 4/2008
• In 2002, reporters managed to smuggle a cylinder of depleted uranium shielded in lead in a suitcase from Vienna to Istanbul via train and in a cargo container through radiation monitors into NY harbor. Cargo was flagged for extra screening, but DU was not sensed.• In 2003, used route Jakarta – LA, same result
6.8 kg DU
• IAEA: During 1993-2006, 275 confirmed incidents with nuclear material and criminal intent; 14 with HEU, 4 with Pu.
Sci. Am.,4/2008
Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 5
A Potential Solution: Muon TomographyA Potential Solution: Muon Tomography
56FeΘ
Θ
Incoming muons (μ±)
μ
Θ
Θ
μ
Note: angles are exaggerated !
(from natural cosmic rays)
Cargo container
hidden &shieldedhigh-Znuclearmaterial
μ tracks
Regular material:small scattering angles
HEU: Big scattering angles!
μQ=+92e
Q=+26e
Main ideas:
• Multiple Coulomb scattering is ~ prop. to Z and could discriminate materials by Z• Cosmic ray muons are ubiquitous; no artificial radiation source or beam needed• Muons are highly penetrating; potential for sensing high-Z material shielded by Fe or Pb • Cosmic Ray Muons come in from many directions allowing for tomographic 3D imaging
235U92
26
)1( 1
with)]/ln(038.01[MeV6.13
00
00 ZZ
XXx
X
x
cp
Approx. Gaussian distribution of scattering angles θ with width θ0:Tracking Detector
Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 6
MT Work by Other GroupsMT Work by Other Groups
J.A. Green et al., “Optimizing the Tracking Efficiency for Cosmic Ray MuonTomography”, LA-UR-06-8497, IEEE NSS 2006
Original idea from Los Alamos (2003): Muon Tomography with Drift Tubes
INFN Padova, Pavia & Genova: Muon Tomographywith spare CMS Muon Barrel Chambers (Drift Tubes)
S. Pesente et al., SORMA West 2008, Berkely, June 2008
Efforts also by Tsinghua U., IHEP Protvino, Decision Science (U.S. commercial)
CMS Muon barrel
BrassCu
Pb W
FeAl
Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 7
Fl. Tech Concept – MT with MPGDsFl. Tech Concept – MT with MPGDs
Use Micro Pattern Gaseous Detectors for tracking cosmic ray muons
ADVANTAGES: excellent spatial resolution improves scattering angle measurement
compact detector structure allows for more compact MT station design
• thin detector layers • small gaps between layers• smaller scattering in detector itself
CHALLENGES:
requires large-area MPGDs (MPGDs as muon detector !)
large number of electronics channels (but occupancies very low)
low rates from cosmics, need good eff.
cost (but access to funding outside HEP)
That’s why we’re here today!
ΘΘ
~ 1 cme-
μ
Readout electronics
Cargo container
hidden &shieldedhigh-Znuclearmaterial
μ tracks
MPGD, e.g. GEM Detector
F. Sauli
MPGD Tracking Detector
MPGD Tracking Detector
Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 8
Where’s Florida Tech ?Where’s Florida Tech ?
Cape Canaveral &NASA Kennedy Space Center
Orlando(IEEE NSS ‘09)
Photo credit: NASA STS-95
Muon Tomography Group:• 2 faculty (HEP, Comp. Sci.)• 1 post-doc• 2 graduate students• 4 undergraduates• (1 electronics engineer)
Small, private university on the “Space Coast”• founded by a physicist in 1958• ~2,500 undergrads & ~2,500 graduate students
Physics & Space Sciences Dept.
Florida Tech
Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 9
Three-year program:
1.Build a Linux cluster for simulation work (160 slots; on Grid via OSG; could be made available to RD51!)
2.Detailed MC simulation of MT station3.Prototyping with increasing detector size4.Performance measurements
Funded by Domestic Nuclear Detection Office (DNDO)in the U.S. Department of Homeland Security (DHS)
(Disclaimer: The views and conclusions contained in this presentation are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Department of Homeland Security.)
R&D ProgramR&D Program
We are currently here
Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 10
Monte Carlo SimulationMonte Carlo Simulation
Basic Target
Muons originate here overan area of 1,000,000 cm2 (1M muons in ~1min exposure)
GEM detectorplanes
Top View5m
3mCRY plane
GEMs
Side View
+ -
• Generate cosmic ray muons with CRY (Lawrence Livermore NL)
• Simulate geometry, target, detector, tracks with GEANT4
• Take advantage of detailed description of multiple scattering effects within GEANT4
(follows Lewis theory of multiple scattering)
3 GEM layers with 5mm gaps between layers
Typical Geometry:
10m
10m
4m
4m
Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 11
Geometrical AcceptanceGeometrical AcceptanceSide View (x-z plane) Top View (x-y plane) MT station type
Top & bottom detectors only
Top, bottom & side detectors
Traversalof stationby cargo
x
y
z
x
y
z
3m
Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 12
• Simple reconstruction algorithm using Point of Closest Approach (“POCA”) of incoming and exiting 3-D tracks
• Treat as single scatter
• Scattering angle:
Scattering ReconstructionScattering Reconstruction
a
b
Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 13
Scattering Angle DistributionsScattering Angle Distributions
Results fromhigh-statisticsMC samples
Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 14
Basic Statistic for Z-discrimination: Basic Statistic for Z-discrimination: Mean Scattering AnglesMean Scattering Angles
Results: • Good Z discrimination (even for Pb vs. U)• Targets imaged• Resolution matters!
Al Fe
W U
Pb
Al Fe
W U
Pb
Al Fe
W U
Pb
Al Fe
W U
Pb
deg][ deg][
deg][ deg][
MT Station & Scenario: •Top, bottom & side det.•40cm 40cm 10cm targets; 5 materials
•Divide volume into voxels
Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 15
Effect of Detector MaterialEffect of Detector MaterialComparison:1. All MT station
materials set to vacuum
2. Station volume filled with air; GEMs modeled by 5mm Kapton material
Result:Minor increase in mean scattering angles and image smearing
deg][ deg][
deg][ deg][
Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 16
Significance of Excess – 10minSignificance of Excess – 10min
• 10 min exposure• Compare targets
against Fe back- ground (steel) using Fe samples w/ high statistics
• Significance for all voxels with an excess at ≥ 99% confidence level over Fe standard:
voxel
Fevoxel
Sig
Sig
Sig
Sig
Sig
W U
Pb
W U
Pb
W U
Pb
W U
Pb> 5σ in ALL high-Z voxels
Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 17
Significance of Excess – 1minSignificance of Excess – 1min
• 1 min exposure• Significance for
all voxels with an excess at ≥ 99% confidence level over Fe standard
• Still doing ok with 50 micron resolution
• With 200 micron resolution we are losing sensitivity
Sig
Sig
Sig
Sig
W U
Pb
W U
Pb
W U
Pb
W U
Pb
Most U voxels > 3σ
Trouble…
Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 18
Identifying Uranium at 99% C.L.Identifying Uranium at 99% C.L.• Test hypothesis that voxels with an excess over Fe actually contain U
• Flag only voxels where mean voxel is within 99% confidence interval around expected mean U for Uranium (based on high-statistics U samples)
1 min exposure10 min exposure
correctpos. ID
false pos.
false pos.
false pos.
W U
Pb some false pos.
false negative !
W U
Pb false positives
correctpos. ID
W U
Pb
W U
Pb
Pb target rejected by U hypothesis !
Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 19
Shielded Targets among Shielded Targets among Stack of Shielding PlatesStack of Shielding Plates
15cm
10cmTargets: 10cm 10cm 10cm U cube
encased by 2.5cm Pb on each side
UPb
15 cm thick shieldingplates made of Al or Fe
Reconstructed scattering angles (normalized)
Al plates
Fe plates
Side Views
Pb
U
10 minexposure
Perfectresolution
“Vertical Clutter” Scenario
Decent Signal
No Signal
Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 20
Advanced Reconstruction AlgorithmAdvanced Reconstruction Algorithm
• Reproducing Los Alamos Expectation Max. algorithm (L. Schultz et al.)• Input: Use lateral shift Δxi in multiple scattering as additional information
on top of scattering angle θi for each (i-th) muon track• Output: Scattering density λkfor each (k-th) voxel of the probed volume
– λ relates the variance of scattering with radiation length (or Z value) of the respective material
• Procedure: Maximize log-likelihood for assignment of scattering densities to all independent voxels given observed tracks
– Analytical derivation leads to an iterative formula for incrementally updating λk values in each iteration
Maximum Likelihood MethodMaximum Likelihood Method
First reconstruction of
40cm 40cm 20cm
U target
Work in Progress…
Δxi
θi
Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 21
Conclusion & PlansConclusion & Plans• Muon Tomography with MPGDs is a promising technology for
detecting shielded nuclear contraband as indicated by our MC studies– Good Z-discrimination expected for
• U vs. Fe with 1 min exposure • U vs. Pb with 10 min exposure
– Resolution and statistics dominate expected performance
• MPGDs – offer significant performance improvement over drift tube stations due
to superior resolution – allow much more compact MT stations
• Plans:– Finalize simulation results; continue developing algorithms (CS people)– Move from simulation to experimentation– Build increasingly large MPGD prototypes and test them for MT– Partner with RD51 collaborators in this development of MPGDs
for large-area muon chambers including electronics development
We expect this experimental program to be a major challenge !