1. An MPGD Application: Muon Tomography for Detection of Nuclear Contraband Marcus Hohlmann, P. Ford, K. Gnanvo, J. Helsby, R. Hoch, D. Mitra Florida Institute of Technology 2 nd meeting of RD51 collaboration, Institute Henri Poincaré, Oct 13, 2008

2. Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 2 Outline Outline 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

3. Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 3 The 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

4. Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 4 Challenge 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

5. Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 5 A Potential Solution: Muon Tomography 56 Fe Θ Θ Incoming muons (μ ± ) μ Θ Θ μ Note: angles are exaggerated ! (from natural cosmic rays) Cargo container hidden & shielded high-Z nuclear material μ tracks Regular material: small scattering angles HEU: Big scattering angles! μ Q=+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 235 U 92 26 Approx. Gaussian distribution of scattering angles θ with width θ 0 : Tracking Detector

6. Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 6 MT 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 Tomography with 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 Brass Cu Pb W Fe Al

7. Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 7 Fl. 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 ! Θ Θ ~ 1 cm e-e- μ Readout electronics Cargo container hidden & shielded high-Z nuclear material μ tracks MPGD, e.g. GEM Detector F. Sauli MPGD Tracking Detector

8. Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 8 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

9. 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 station 3.Prototyping with increasing detector size 4.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 Program We are currently here

10. Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 10 Monte Carlo Simulation Basic Target Muons originate here over an area of 1,000,000 cm 2 (1M muons in ~1min exposure) GEM detector planes Top View 5m 3m CRY 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 4m

11. Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 11 Geometrical Acceptance Side View (x-z plane) Top View (x-y plane) MT station type Top & bottom detectors only Top, bottom & side detectors Traversal of station by cargo x y z x y z 3m

12. 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 Reconstruction

13. Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 13 Scattering Angle Distributions Results from high-statistics MC samples

14. Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 14 Basic Statistic for Z-discrimination: Mean Scattering Angles Results: Good Z discrimination (even for Pb vs. U) Targets imaged Resolution matters! AlFe WU Pb AlFe WU Pb AlFe W U Pb AlFe W U Pb MT Station & Scenario: Top, bottom & side det. 40cm  40cm  10cm targets; 5 materials Divide volume into voxels

15. Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 15 Effect of Detector Material Comparison: 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

16. Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 16 Significance 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: Sig W U Pb W U W U W U > 5σ in ALL high-Z voxels

17. Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 17 Significance 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 W U Pb W U W U W U Most U voxels > 3σ Trouble…

18. Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 18 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 exposure 10 min exposure correct pos. ID false pos. false pos. W U Pb some false pos. false negative ! W U Pb false positives correct pos. ID W U Pb W U Pb target rejected by U hypothesis !

19. Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 19 Shielded Targets among Stack of Shielding Plates 15cm 10cm Targets: 10cm  10cm  10cm U cube encased by 2.5cm Pb on each side U Pb 15 cm thick shielding plates made of Al or Fe Reconstructed scattering angles (normalized) Al plates Fe plates Side Views Pb U 10 min exposure Perfect resolution “Vertical Clutter” Scenario Decent Signal No Signal

20. Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 20 Advanced Reconstruction Algorithm Reproducing Los Alamos Expectation Max. algorithm (L. Schultz et al.) Input: Use lateral shift Δ x i in multiple scattering as additional information on top of scattering angle θ i for each (i-th) muon track Output: Scattering density λ k for 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 λ k values in each iteration Maximum Likelihood Method First reconstruction of 40cm  40cm  20cm U target Work in Progress… ΔxiΔxi   θiθi

21. Oct 13, 2008 M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris 21 Conclusion & 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 !