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 !