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

Recent news… 10/1/ th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann 2 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. 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. …

… on an old problem 10/1/ th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann 3 Colorado Sen. Eugene Millikin pressed 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

μ μ FeU Large Scattering Small Scattering μ Iron Small Scattering Uranium μ Large Scattering μ μ Incoming muons (from natural cosmic rays) Note: Angles Exaggerated! Tracking detectors Multiple Coulomb scattering to 1 st order produces Gaussian distribution of scattering angles θ with width σ = Θ 0 : Towards a solution… 10/1/ th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann 4 Muon Tomography Concept:

Growing Interest in MT 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 10/1/ th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann 5 8 MT presentations scheduled at upcoming IEEE NSS:

 1 ft 3 active volume 8 30cm  30cm GEMs Fl. Tech Cubic-Foot MT Prototype GEM Muon Tomography 10/1/ th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann 6 30cm × 30cm Triple-GEMs with x-y readout Event display of 141 reconstructed tracks probing target Trigger scintillators X-Z view Y-Z view World’s largest RD51 SRS application (12,288 channel APV readout w/ DATE & AMORE)

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 Track & Image Reconstruction Detector hits formed 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 (< 2 o ) Scattering point reconstruction using Point Of Closest Approach of incoming and exiting segment in 3d Find in voxels in volume Remove isolated scattering pixels; keep clustered scattering pixels 7 DOCA Object DOCA unbiased residuals V measured scattering angle Ref.: Michael Staib, M.S. thesis

Number of POCA points Mean Scattering Angle Removing isolated pixels (NNP) Reco & Image Processing Steps 10/1/ th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann 8 Not aligned Aligned M. Staib, M.S. thesis

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 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 10/1/ th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann 9

Unshielded Materials 10/1/ th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann 10 U W Pb Fe Sn Top View Side views in 3 vertical planes: → → → Mean Scattering Angle (2mm×2mm×40mm voxel) 6mm Al cladding for U Pb W U Sn Fe 164,323 total reconstructed tracks Number Neighboring Pixel Cut > 5

Horizontal Imaging Resolution 10/1/ th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann 11 0 mm 2 mm 115,834 Tracks 94,719 Tracks 111,036 Tracks Gap starts to become visible with ≥ 6 mm spacing 4 mm Lead Tungsten 0 mm8 mm 2 mm increments 8 mm6 mm 107,506 Tracks 121,634 Tracks Gap begins to become visible with ≥ 6 mm spacing in y 115,834 Tracks M. Staib, M.S. thesis

Horizontal Imaging Resolution 10/1/ th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann 12 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

Vertical Imaging Resolution 10/1/ th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann 13 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 Gap begins to become visible with ≥ 45 mm spacing in z 160,096 tracks 235,836 tracks201,836 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. Z Z Z

Uranium Shielded w/ Bronze 187,731 reconstructed tracks Number Neighboring Pixel Cut > 10 2 mm x 2 mm x 40 mm voxels 40 mm XY slices descending in Z by 5 mm per frame 10/1/ th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann 14 Shielding made of tin-bronze (83% Cu, 7% Sn, 7% Pb, 3% Zn) with X 0 = 1.29 cm & 1.7 cm walls 1.7cm DU M. Staib, M.S. thesis

With Lead Shielding Lead Tantalum Tungsten Uranium Tin Iron 10/1/ th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann 15 Lead box with 3.4mm thick walls placed inside

Muon Tomogram The shielded targets are clearly visible in the reconstruction Lead Tantalum Tungsten Uranium Tin Iron 292,555 reconstructed tracks NNP cut = 5 2 mm x 2 mm x 40 mm voxels 10/1/ th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann mm XY slices descending in Z by 5 mm per frame M. Staib, M.S. thesis

More Pb Shielding 10/1/ th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann 17 Add two more Pb plates to the top of the box, for a total of 10mm of Pb top shielding: Well imaged in x-y plane 397,362 reconstructed tracks NNP cut = 5

3mm vs. 10mm Pb top shielding 10/1/ th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann 18 Side view: Lead Tantalum Tungsten Uranium Tin Iron Vertical slice in this plane 3.4 mm top shielding 10 mm top shielding Pb W Ta outline of Pb shielding box

Z-discrimination for shielded cubes 10/1/ th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann 19 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/  X 0 X 0 ( ) normalized to 1000 rec. tracks

Where is the limit? 10/1/ th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann 20 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

Spatial sensitivity bias 10/1/ th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann 21 Top View Mean Scatterin g Angle U W Pb Fe Sn 164,323 total reconstructed tracks Now flip position of U and Pb: 183,051 total reconstructed tracks Pb U U right tomogram left tomogram

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

Benefit from side detectors 10/1/ th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann 23 Three identical lead-acid UPS batteries in MTS Tracks through top & bottom GEMs only Tracks through top & bottom GEMs plus top & side GEMs plus bottom & side GEMs Side detectors help extend acceptance towards edges of MTS (as expected) GEM-MTS is only MTS operating with side detectors

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 10/1/ th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann 24

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!