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

GEM-based Muon Tomography

of Shielded High-Z Materials

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

Marcus HohlmannFlorida Institute of Technology

Recent news…Recent news…

10/1/2012 10th 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 problemon an old problem


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

μμ

Fe ULarge

ScatteringSmall

Scattering

μIron

Small Scattering

Uraniumμ

LargeScattering

μμ Incoming muons (from natural cosmic rays)

Note: Angles Exaggerated!

)]/ln(038.01[MeV6.130

0

0 XxXx

cp

Tracking detectors

Multiple Coulomb scattering to 1st order produces Gaussian distribution of scattering angles θ with width σ = Θ0 :

𝑋0 = 716.4 g cm-2 ∙AZሺZ + 1ሻln (287 ξ𝑍Τ )

Towards a solution…Towards a solution…


Muon Tomography Concept:

Growing Interest in MTGrowing 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


8 MT presentations scheduled at upcoming IEEE NSS:

1 ft3

active

volume8 30cm 30cm GEMs

Fl. Tech Cubic-Foot MT Prototype

GEM Muon TomographyGEM Muon Tomography


30cm × 30cmTriple-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 ReconstructionTrack & 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 (< 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

7

DOCA

Object

DOCA

unbiasedresiduals

Vmeasuredscattering

angle

Ref.: Michael Staib, M.S. thesis

Number of POCA points Mean Scattering Angle Removing isolated pixels (NNP)

Reco & Image Processing StepsReco & Image Processing Steps


Not aligned

Aligned

M. Staib, M.S. thesis

Current R&D FocusCurrent R&D FocusSystematic 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


Unshielded MaterialsUnshielded Materials


U

WPb

FeSn

Top View

Side views in 3 vertical planes:

→→→

MeanScatteringAngle (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 ResolutionHorizontal Imaging Resolution


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 Lead

Tungsten Tungsten

0 mm 8 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


Horizontal Imaging ResolutionHorizontal 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.


Vertical Imaging ResolutionVertical 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

Gap begins to become visiblewith ≥ 45 mm spacing in z

160,096 tracks 235,836 tracks 201,836 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/ BronzeUranium 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


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

1.7cm

DU


With Lead ShieldingWith Lead Shielding

LeadTantalum

Tungsten

UraniumTin Iron


Lead box with 3.4mm thick walls

placed inside

Muon TomogramMuon Tomogram

The shielded targets are clearly visible in the reconstruction

LeadTantalum

Tungsten

UraniumTin Iron

• 292,555 reconstructed tracks• NNP cut = 5• 2 mm x 2 mm x 40 mm voxels


40 mm XY slices descending in Z by 5 mm per frame


More Pb ShieldingMore Pb Shielding


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 shielding3mm vs. 10mm Pb top shielding


Side view:

LeadTantalum

Tungsten

UraniumTin Iron

Vertical slice in this plane

3.4 mm top shielding 10 mm top shielding

Pb WTa

outline of Pb shielding box

Z-discrimination for shielded cubesZ-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

X0 ( )

)]/ln(038.01[MeV6.130

0

0 XxXx

cp

normalized to1000 rec. tracks

Where is the limit? 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

Spatial sensitivity biasSpatial sensitivity bias


Top View

MeanScatteringAngle

U

WPb

FeSn


Now flip position of U and Pb:


Pb

PbU

U

right tomogramleft tomogram

Towards an unbiased sensitivityTowards an unbiased sensitivity


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 detectorsBenefit from side detectors


Three identical lead-acid UPS batteries in MTS

Tracks through top & bottom GEMs onlyTracks 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 & ConclusionsSummary & 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 expected10/1/2012 10th RD51 Coll. Meeting, Stony Brook U. - Marcus Hohlmann 24

Thank you for your time!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!

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

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