Transcript Gas Electron Multiplier (GEM) - a novel particle detector

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
2nd meeting of RD51 collaboration, Institute Henri Poincaré, Oct 13, 2008
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
M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris
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
M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris
Challenge in Detecting Nuclear Contraband
~ 800 Radiation Portal Monitors (n,γ) in U.S.
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
Sci. Am.,4/2008
6.8 kg DU
• IAEA: During 1993-2006, 275 confirmed incidents with
nuclear material and criminal intent; 14 with HEU, 4 with Pu.
HEU can be hidden
from conventional
radiation monitoring
because emanating
radiation is relatively
easy to shield within
regular cargo
M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris
Scientific American, April 2008
A Potential Solution: Muon Tomography
Incoming muons
(μ±)
Note: angles are exaggerated !
(from natural cosmic rays)
Q=+92e
μ
μ
Q=+26e
Θ
235
92U
Θ
56
26 Fe
Regular material:
small scattering angles
hidden &
shielded
Θ
high-Z
nuclear
material
Θ
μ
HEU: Big
scattering angles!
Approx. Gaussian distribution
of scattering angles θ with width θ0:
Main ideas:
μ tracks
0 
13.6 MeV x
1
[1  0.038ln(x / X 0 )] with
 Z ( Z  1)
cp
X0
X0
• 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
M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris
MT Work by Other Groups
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)
CMS Muon barrel
J.A. Green et al., “Optimizing the
Tracking Efficiency for Cosmic Ray
MuonTomography”, LA-UR-06-8497,
IEEE NSS 2006
S. Pesente et al.,
SORMA West 2008,
Berkely, June 2008
Pb W
Brass
Cu
Efforts also by Tsinghua U., IHEP Protvino,
Decision Science (U.S. commercial)
M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris
Fe
Al
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
hidden &
shielded
CHALLENGES:
 requires large-area MPGDs
(MPGDs as muon detector !)
Θ
high-Z
nuclear
material
μ
Θ
MPGD, e.g. GEM Detector
 large number of electronics
channels (but occupancies very low)
~ 1 cm
μ tracks
e-
 low rates from cosmics, need good eff.
 cost (but access to funding outside HEP)
That’s why we’re here today!
M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris
Readout electronics
F. Sauli
Where’s Florida Tech ?
Cape Canaveral &
NASA Kennedy Space Center
Orlando
(IEEE NSS ‘09)
Florida Tech
Photo credit: NASA STS-95
Physics & Space Sciences Dept.
Small, private university on the “Space Coast”
• founded by a physicist in 1958
• ~2,500 undergrads & ~2,500 graduate students
Muon Tomography Group:
• 2 faculty (HEP, Comp. Sci.)
• 1 post-doc
• 2 graduate students
• 4 undergraduates
• (1 electronics engineer)
M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris
R&D Program
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
We are currently here
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.)
M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris
Monte Carlo Simulation
Typical Geometry:
• Generate cosmic ray
muons with CRY
Side View
10m
(Lawrence Livermore NL)
• Simulate geometry,
target, detector, tracks
with GEANT4
Muons originate here over
an area of 1,000,000 cm2
(1M muons in ~1min exposure)
4m
GEM
detector
planes
Basic Target
• 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
Top View
10m
5m
+
-
4m
3m
GEMs
M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris
CRY plane
Geometrical Acceptance
MT station type
Top View (x-y plane)
Side View (x-z plane)
Top & bottom detectors only
z
3m
y
x
Top, bottom & side detectors
z
y
x
Traversal
of station
by cargo
M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris
Scattering Reconstruction
• Simple reconstruction
algorithm using Point
of Closest Approach
(“POCA”) of incoming
and exiting 3-D tracks
• Treat as single scatter
• Scattering angle:

a

M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris

b
Scattering Angle Distributions
Results from
high-statistics
MC samples
M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris
Basic Statistic for Z-discrimination:
Mean Scattering Angles
MT Station & Scenario:
•Top, bottom & side det.
•40cm  40cm  10cm
targets; 5 materials
•Divide volume into voxels
 [deg]
 [deg]
W
U
W
Pb
Al
U
Pb
Fe
Al
Fe
 [deg]
W
Results:
• Good Z discrimination
(even for Pb vs. U)
• Targets imaged
• Resolution matters!
U
 [deg]
W
Pb
Al
U
Pb
Fe
Al
M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris
Fe
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
 [deg]
 [deg]
 [deg]
 [deg]
Result:
Minor increase in
mean scattering
angles and image
smearing
M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris
Significance of Excess – 10min
• 10 min exposure
• Compare targets
against Fe background (steel)
using Fe samples
w/ high statistics
• Significance for
all voxels with an
excess at ≥ 99%
confidence level
over Fe standard:
Sig 
voxel  Fe
Sig
Sig
W
U
U
W
Pb
Pb
> 5σ in ALL high-Z voxels
Sig
U
W
Pb
Sig
U
W
Pb

voxel
M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris
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
Sig
U
W
U
W
Pb
Pb
Most U voxels > 3σ
Sig
U
W
Pb
Sig
U
W
Pb
Trouble…
M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris
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
W
U
Pb
W
U
false Pb
pos.
correct
pos. ID
Pb target rejected
by U hypothesis !
W
Pb
false
positives
U
W
U
some Pb
false
pos.
correct
pos. ID
false pos.
false pos.
M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris
false negative !
Shielded Targets among
Stack of Shielding Plates
Reconstructed scattering angles (normalized)
Side
Views
Al plates
U
Pb
10 min
exposure
Perfect
resolution
Decent
Signal
15cm
Targets: 10cm  10cm  10cm U cube
encased by 2.5cm Pb on each side
10cm
Pb
U
Fe plates
15 cm thick
shielding
plates made
of Al or Fe
“Vertical Clutter” Scenario
M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris
No Signal
Advanced Reconstruction Algorithm
Maximum Likelihood Method
• Reproducing Los Alamos Expectation Max. algorithm (L. Schultz et al.)
• Input: Use lateral shift Δxi in multiple scattering as additional information
on top of scattering angle θi for each (i-th) muon track
• Output: Scattering density λkfor 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 λk values in each iteration

θi

Δxi
Work in
Progress…
M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris
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
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 !
M. Hohlmann - Muon Tomography, RD51 Collaboration meeting, IHP, Paris
due