Gas Electron Multiplier (GEM) - a novel particle detector for High Energy Astrophysics

GEM-basedMuon Tomography of Shielded High-Z Materials

10th RD51 Collaboration Meeting, Stony Brook U., Oct 1, 2012

Marcus HohlmannFlorida Institute of Technology

1Recent news10/1/201210th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann2

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 nations 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 departments 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 problem10/1/201210th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann3Colorado 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 ArchivesThat 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, 2/18/07FeULargeScatteringSmall Scattering

IronSmall Scattering

UraniumLargeScatteringIncoming muons (from natural cosmic rays)Note: Angles Exaggerated!

Tracking detectorsMultiple Coulomb scattering to 1st order produces Gaussian distribution of scattering angles with width = 0 :

Towards a solution10/1/201210th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann4Muon Tomography Concept:Growing Interest in MTMuon Tomography withDrift Tubes Decision Sciences Intl Corp., commercial effort, US (now operating full-size MT prototype at Freeport, Bahamas)GEMsFlorida Tech, USPlastic Scintillators CRIPT Consortium, CanadaINFN Catania, ItalyMulti-gap RPCs Tsinghua U., China

10/1/201210th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann58 MT presentations scheduled at upcoming IEEE NSS:

1 ft3

activevolume8 30cm 30cm GEMs

Fl. Tech Cubic-Foot MT Prototype GEM Muon Tomography10/1/201210th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann630cm 30cmTriple-GEMswith x-y readoutEvent display of 141 reconstructed tracks probing targetTrigger scintillators

X-Z viewY-Z viewWorlds 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 ReconstructionDetector hits formed from readout strip clustersAll hit combinations within each of the four tracking stations (t, b, l, r) track segment candidatesTrack with smallest distance of closest approach (DOCA) of incoming and exiting segments in 3d is selected as best trackDetector 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 3dFind in voxels in volumeRemove isolated scattering pixels; keep clustered scattering pixels

7

DOCA

ObjectDOCAunbiasedresidualsVmeasuredscatteringangleRef.: Michael Staib, M.S. thesis

Number of POCA pointsMean Scattering AngleRemoving isolated pixels (NNP)Reco & Image Processing Steps10/1/201210th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann8Not alignedAlignedM. Staib, M.S. thesisCurrent R&D FocusSystematic Performance Studies of GEM-based MT: Imaging StudiesHow 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-discriminationCan 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 runningOther MT efforts have shown that detection presence of some high-Z material can be done in a few minutes; will address later

10/1/201210th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann9

Unshielded Materials10/1/201210th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann10

UWPbFeSnTop ViewSide views in 3 vertical planes:MeanScatteringAngle (2mm2mm40mm voxel)6mm Al cladding for U

PbWUSnFe164,323 total reconstructed tracks

Number Neighboring Pixel Cut > 5Horizontal Imaging Resolution10/1/201210th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann11

0 mm2 mm115,834 Tracks94,719 Tracks

111,036 TracksGap starts to become visible with 6 mm spacing4 mm

LeadLeadTungstenTungsten0 mm8 mm2 mm increments

8 mm6 mm107,506 Tracks121,634 TracksGap begins to become visiblewith 6 mm spacing in y115,834 TracksM. Staib, M.S. thesisHorizontal Imaging Resolution10/1/201210th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann12

No significant signal with 0 mm, 2 mm, or 4 mm gap spacingSignificant 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. thesisVertical Imaging Resolution10/1/201210th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann13

Analogous test with vertical gaps (Pb cube stacked on top of W cube):15 mm vertical gap30 mm vertical gap45 mm vertical gapGap begins to become visiblewith 45 mm spacing in z160,096 tracks235,836 tracks201,836 tracksWe conclude that the lower limit on the spatial imaging resolution in the ZX plane with ~200k total reconstructed MTS tracks is currently 45 mm.ZZZUranium Shielded w/ Bronze

187,731 reconstructed tracksNumber Neighboring Pixel Cut > 102 mm x 2 mm x 40 mm voxels

40 mm XY slices descending in Z by 5 mm per frame10/1/201210th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann14

Shielding made of tin-bronze(83% Cu, 7% Sn, 7% Pb, 3% Zn) with X0 = 1.29 cm & 1.7 cm walls

1.7cmDUM. Staib, M.S. thesisWith Lead Shielding

LeadTantalumTungstenUraniumTinIron10/1/201210th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann15Lead box with 3.4mm thick wallsplaced insideMuon Tomogram

The shielded targets are clearly visible in the reconstruction

LeadTantalumTungstenUraniumTinIron292,555 reconstructed tracksNNP cut = 52 mm x 2 mm x 40 mm voxels10/1/201210th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann1640 mm XY slices descending in Z by 5 mm per frameM. Staib, M.S. thesisMore Pb Shielding10/1/201210th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann17Add two more Pb plates to the top of the box, for a total of 10mm of Pb top shielding:

Well imaged in x-y plane397,362 reconstructed tracksNNP cut = 53mm vs. 10mm Pb top shielding10/1/201210th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann18Side view:

LeadTantalumTungstenUraniumTinIronVertical slice in this plane3.4 mm top shielding10 mm top shieldingPbWTaoutline of Pb shielding boxZ-discrimination for shielded cubes10/1/201210th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann19Define 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/X0X0 ()

normalized to1000 rec. tracksWhere is the limit? 10/1/201210th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann20Place U cube inside a shielding structure with ~ 2cm Pb plates at top, bottom, and 2 sides:335,410 rec. tracksNNP cut = 5

U cube still discernible

Spatial sensitivity bias10/1/201210th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann21

Top ViewMeanScatteringAngle

UWPbFeSn164,323 total reconstructed tracksNow flip position of U and Pb:183,051 total reconstructed tracksPbPbUU

right tomogramleft tomogramTowards an unbiased sensitivity10/1/201210th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann22Mainly 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 tracksNNP cut = 1Benefit from side detectors10/1/201210th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann23

Three identical lead-acid UPS batteries in MTSTracks through top & bottom GEMs onlyTracks through top & bottom GEMs plus top & side GEMs plus bottom & side GEMsSide detectors help extend acceptance towards edges of MTS (as expected)GEM-MTS is only MTS operating with side detectorsSummary & ConclusionsGEM-based MTS prototype taking lots of data!Without shielding, U can clearly be discriminated from Pb, quite possibly from WHigh-Z materials clearly discriminated from medium-Z materials even when (moderately) shieldedImaging 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 sensitivitySide detectors help mainly near the edge of the MTS as expected

10/1/201210th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann24Thank 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!