GEM-based Muon T omography of S hielded H igh-Z Materials

1. 10th RD51 Collaboration Meeting, Stony Brook U., Oct 1, 2012 GEM-based Muon Tomography of Shielded High-Z Materials Marcus HohlmannFlorida Institute of Technology

2. Recent news… The Department of Homeland Security was given until this month to ensure that 100 percent of inbound shipping containers are screened at foreign ports. But the department’s secretary, Janet Napolitano, informed Congress in May that she was extending a two-year blanket exemption to foreign ports because the screening is proving too costly and cumbersome. She said it would cost $16 billion to implement scanning measures at the nearly 700 ports worldwide that ship to the United States. Instead, the DHS relies on intelligence-gathering and analysis to identify “high-risk” containers, which are checked before being loaded onto ships. Under this system, fewer than half a percent of the roughly 10 million containers arriving at U.S. ports last year were scanned before departure. The DHS says that those checks turned up narcotics and other contraband but that there have been no public reports of smuggled nuclear material. … The DHS says monitors scan 99 percent of the containers for radiation after they arrive at U.S. ports. But experts say the monitors at U.S. ports are not sophisticated enough to detect nuclear devices or highly enriched uranium, which emit low levels of radiation. … By Douglas Frantz, Updated: Sunday, July 15, 4:05 PM The Obama administration has failed to meet a legal deadline for scanning all shipping containers for radioactive material before they reach the United States, a requirement aimed at strengthening maritime security and preventing terrorists from smuggling a nuclear device into any of the nation’s 300 sea and river ports. 10th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann

3. … on an old problem Colorado Sen. Eugene Millikinpressed Oppenheimer about how to find a bomb hidden in a city: Sen. Millikin: “We... have mine-detecting devices, which are rather effective... I was wondering if anything of that kind might be available to use as a defense against that particular type of use of atomic bombs.” Dr. Oppenheimer: “If you hired me to walk through the cellars of Washington to see whether there were atomic bombs, I think my most important tool would be a screwdriver to open the crates and look. I think that just walking by, swinging a little gadget would not give me the information.” Transcripts from the National Archives That candid assessment shocked the senators, who then asked the Atomic Energy Commission to examine the problem. Robert Hofstadter and Wolfgang Panofsky, a veteran of the Manhattan Project team that built the atomic bomb, produced a still-classified assessment, which came to be known as the “Screwdriver Report”. Panofsky, now the director emeritus of the Stanford Linear Accelerator Center, says the assignment was to detect 1 cubic inch of highly enriched uranium or plutonium hidden inside a crate and smuggled across a land border. "The conclusions of that report are still valid because the laws of physics have not changed one bit," Panofsky tells U.S. News. "You still can't detect a nuclear device unless you are, say, 10 feet away from it - and even then it can be quite easily shielded." US News & World Report, 2/18/07 10th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann

4. Towards a solution… μ μ Incoming muons (from natural cosmic rays) μ μ Muon Tomography Concept: Uranium Iron μ μ Fe U Small Scattering Large Scattering Tracking detectors Small Scattering Large Scattering Note: Angles Exaggerated! Multiple Coulomb scattering to 1st order produces Gaussian distribution of scattering angles θwith width σ= Θ0 : Where may be approximated by 10th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann

5. Growing Interest in MT 8 MT presentations scheduled at upcoming IEEE NSS: Muon Tomography with • Drift Tubes • Decision Sciences Int’l Corp., commercial effort, US (now operating full-size MT prototype at Freeport, Bahamas) • GEMs • Florida Tech, US • Plastic Scintillators • CRIPT Consortium, Canada • INFN Catania, Italy • Multi-gap RPCs • Tsinghua U., China 10th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann

6. GEM Muon Tomography Event display of 141 reconstructed tracks probing target 1 ft3 active volume X-Z view Y-Z view 8 30cm  30cm GEMs Trigger scintillators World’s largest RD51 SRS application (12,288 channel APV readout w/ DATE & AMORE) Fl. Tech Cubic-Foot MT Prototype 30cm × 30cm Triple-GEMs with x-y readout 10th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann

7. Track & Image Reconstruction • Detector hitsformed from readout strip clusters • All hit combinations within each of the four tracking stations (t, b, l, r) → track segment candidates • Track with smallest distance of closest approach (DOCA) of incoming and exiting segments in 3d is selected as best track • Detector alignment using tracks crossing an empty MT station • Remove low-angle scattering (< 2o) • Scattering point reconstruction using Point Of Closest Approach of incoming and exiting segment in 3d • Find <scatter> in voxels in volume • Remove isolated scattering pixels; keep clustered scattering pixels DOCA V unbiased residuals • Number in Neighboring Pixels (NNP): add number of POCA in 8 voxels surrounding voxel V • If NNP < some • threshold, remove • contents of V. • Repeat for all voxels DOCA Object measured scattering angle Ref.: Michael Staib, M.S. thesis

8. Reco & Image Processing Steps Not aligned Number of POCA points Mean Scattering Angle Removing isolated pixels (NNP) Aligned M. Staib, M.S. thesis 10th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann

9. Current R&D Focus Systematic Performance Studies of GEM-based MT: • Imaging Studies • How well can we resolve material shapes? • What is the (ultimate) imaging resolution? • What is the image quality with (substantial) shielding? • How much information are we gaining by having added the side detectors? • How do results depend on the target location within the MT volume? • Z-discrimination • Can we tell U from medium-Z material? • Can we distinguish high-Z materials from each other? (U from W, Pb)? • Less emphasis on “How fast can you detect”? • Typical MT images shown here take 24-48 hrs. of running • Other MT efforts have shown that detection presence “of some high-Z material” can be done in a few minutes; will address later 10th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann

10. Unshielded Materials Mean Scattering Angle (2mm×2mm×40mm voxel) Top View → → → • 164,323 total reconstructed tracks • Number Neighboring Pixel Cut > 5 6mm Al cladding for U Side views in 3 vertical planes: Pb W U U Pb Sn W Fe Sn Fe 10th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann

11. Horizontal Imaging Resolution 0 mm 2 mm 111,036 Tracks 115,834 Tracks 94,719 Tracks 0 mm 8 mm Lead Lead 115,834 Tracks 6 mm 8 mm 4 mm 121,634 Tracks 107,506 Tracks 2 mm increments Gap begins to become visible with ≥ 6 mm spacing in y Gap starts to become visible with ≥ 6 mm spacing Tungsten Tungsten M. Staib, M.S. thesis 10th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann

12. Horizontal Imaging Resolution No significant signal with 0 mm, 2 mm, or 4 mm gap spacing Significant signal for a gap begins to develop with 6 mm spacing: We conclude that the lower limit on the spatial imaging resolution in the XY plane with ~100k total reconstructed MTS tracks is currently 6 mm. M. Staib, M.S. thesis 10th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann

13. Vertical Imaging Resolution Analogous test with vertical gaps (Pb cube stacked on top of W cube): 15 mm vertical gap 30 mm vertical gap 45 mm vertical gap Z Z Z Gap begins to become visible with ≥ 45 mm spacing in z 160,096 tracks 201,836 tracks 235,836 tracks We conclude that the lower limit on the spatial imaging resolution in the ZX plane with ~200k total reconstructed MTS tracks is currently 45 mm. 10th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann

14. Uranium Shielded w/ Bronze 40 mm XY slices descending in Z by 5 mm per frame Shielding made of tin-bronze (83% Cu, 7% Sn, 7% Pb, 3% Zn) with X0 = 1.29 cm & 1.7 cm walls DU 1.7cm • 187,731 reconstructed tracks • Number Neighboring Pixel Cut > 10 • 2 mm x 2 mm x 40 mm voxels M. Staib, M.S. thesis 10th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann

15. With Lead Shielding Lead box with 3.4mm thick walls Tantalum placed inside Lead Tungsten Tin Uranium Iron 10th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann

16. Muon Tomogram 40 mm XY slices descending in Z by 5 mm per frame The shielded targets are clearly visible in the reconstruction Tantalum Lead Tungsten Tin Uranium Iron • 292,555 reconstructed tracks • NNP cut = 5 • 2 mm x 2 mm x 40 mm voxels M. Staib, M.S. thesis 10th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann

17. More Pb Shielding Add two more Pb plates to the top of the box, for a total of 10mm of Pb top shielding: • 397,362 reconstructed tracks • NNP cut = 5 Well imaged in x-y plane 10th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann

18. 3mm vs. 10mm Pb top shielding Side view: Vertical slice in this plane 3.4 mm top shielding 10 mm top shielding Tantalum outline of Pb shielding box Lead Tungsten Pb W Ta Tin Uranium Iron 10th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann

19. Z-discrimination for shielded cubes Define a “simple scattering density” to discriminate shielded target materials: Sum of all scattering angles measured within a target / volume of target cube (normalized to # of rec. tracks) Fit to 1/X0 normalized to 1000 rec. tracks X0 ( ) 10th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann

20. Where is the limit? Place U cube inside a shielding structure with ~ 2cm Pb plates at top, bottom, and 2 sides: • 335,410 • rec. tracks • NNP cut = 5 U cube still discernible 10th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann

21. Spatial sensitivity bias left tomogram right tomogram Mean Scattering Angle Now flip positionof U and Pb: U Pb Pb W Pb U U Sn Fe • 183,051 total reconstructed tracks • 164,323 total reconstructed tracks Top View 10th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann

22. Towards an unbiased sensitivity Three identical lead-acid UPS batteries in MTS: Mainly a geometric acceptance effect Beginnings of mapping out sensitivity within the volume of the MTS to correct for bias towards center… • 102,679reconstructed tracks • NNP cut = 1 10th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann

23. Benefit from side detectors Three identical lead-acid UPS batteries in MTS Tracks through top & bottom GEMs plus top & side GEMs plus bottom & side GEMs Tracks through top & bottom GEMs only • Side detectors help extend acceptance towards edges of MTS (as expected) • GEM-MTS is only MTS operating with side detectors 10th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann

24. Summary & Conclusions • GEM-based MTS prototype taking lots of data! • Without shielding, U can clearly be discriminated from Pb, quite possibly from W • High-Z materials clearly discriminated from medium-Z materials even when (moderately) shielded • Imaging resolutions measured to be ~6 mm in the horizontal and ~45 mm in the vertical (w/o shielding) • First measurements of expected spatial biases on sensitivity • Side detectors help mainly near the edge of the MTS as expected 10th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann

25. Thank you for your time! Acknowledgements: This work is currently being pursued mainly by our students. Thanks to grad students Mike Staib, Vallary Bhopatkar, and Lenny Grasso, and undergraduates Mike Phipps, Jessie Twigger, and Christian Zelenka!