Detection of
Special Nuclear Materials
Alexander Glaser
WWS556d
Princeton University
April 16, 2007
Revision 6
1
J. Kammeraad et al., Radiological and Nuclear Countermeasures
Department of Homeland Security, Briefing, 9 March 2004
2
J. Kammeraad et al., Radiological and Nuclear Countermeasures
Department of Homeland Security, Briefing, 9 March 2004
3
J. Kammeraad et al., Radiological and Nuclear Countermeasures
Department of Homeland Security, Briefing, 9 March 2004
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Detector Technology
(main systems currently being acquired by DHS/DNDO)
Advanced Spectroscopic Portal (ASP)
Spectroscopic analysis to reduce false alarms (“nuisance alarms”)
due to normally occurring radioactive material (NORM)
DNDO awarded contracts to three companies in July 2006
Total cost: $1.1 billion over a five-year period
Several variants of the ASP
(fixed-site, truck-mounted, and shuttle carrier-mounted systems)
Cargo Advanced Automated Radiography System (CAARS)
Detection of high-density material in cargo
(Potential shielding for nuclear material to evade passive detection)
DNDO awarded contracts to three companies in September 2006
Prototypes expected by mid-2009
Statement before the House Science Committee by Vayl S. Oxford, 8 March 2007
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The “Verification of Shielded SNM” Advanced Technology Demonstration
(ATD), with final system design review expected in late FY 2009, “will
develop and test advanced technology to resolve alarms and definitely
verify the presence of SNM despite cluttered environments or intentional
countermeasures like shielding.”
“The Department of Homeland Security’s R&D Budget Priorities for Fiscal Year 2008”
Opening Statement by Vayl S. Oxford (Director DNDO, DHS)
before the House Science Committee
Subcommittee on Technology and Innovation
8 March 2007
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Detection Modes & Techniques
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Detection Modes
LOOK FOR
NEUTRONS
passive
PHOTONS
(gammas)
detection
USE
LOOK FOR
NEUTRONS
active
NEUTRONS
interrogation
PHOTONS
(gammas)
PHOTONS
(gammas)
NEUTRONS
PHOTONS
(x-rays)
PHOTONS
(imaging)
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The Detection Dilemma
Passive modes
Usability
Performance
simple and safe
rather ineffective
against shielded SNM
(in particular, HEU)
Active modes
cannot be used in
many circumstances
able to trigger characteristic response by SNM
(e.g. dose to humans)
(e.g. fission)
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Passive Detection
(of highly enriched uranium by its gamma radiation)
Plutonium can be passively
detected by its neutron emissions
NOT DISCUSSED BELOW
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Decay Chains
(simplified and incomplete)
Actinium Series
Radium Series
Pu-239
Pu-242
U-235
U-238
Pu-238
Pa-234m
Th-231
Pa-231
U-234
Th-234
Pa-234
Ac-227
Th-227
Th-230
The most valuable gamma emission for detection purposes is a 1.001 MeV line of protactinium-234m
(decay product of U-238, i.e. not U-235)
About 100 gammas per second and gram of U-238 at 1.001 MeV
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Passive Detection of SNM
External Shielding
Detector
Special Nuclear Material
Total
emission rate
Attenuation
factors
S = (I × M ) (G × F )
Detectable
fraction
!
AD
4πR2
"
Efficiency
of detector
SB = B AD !
Detector background
"
!
"
!
"
#$
3
4
1 − exp − µ r
with G ≈
and F = exp − λ d
4µr
3
Self-shielding
for solid sphere of radius r
External shielding
of thickness d
S TM
!
> m SB T M
Criterion for detection of material
Minimum TM for given distance
or maximum distance R for given TM
This discussion follows: S. Fetter, V. A. Frolov, M. Miller, R. Mozley, O. F. Prilutsky, S. N. Rodionov, and R. Z. Sagdeev, “Detecting Nuclear Warheads,”
Science & Global Security, Vol. 1, Nos. 3-4, 1990, pp. 225-253
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Passive Detection of SNM
12 kg HEU
(clean, 7% U-238)
Gamma radiation
84,500/s at 1.001 MeV
Self-shielding of sphere
G = 0.10 for µ = 1.41/cm
EXTERNAL SHIELDING (10 cm of lead)
Correction
F = 0.00045 for λ = 0.77/cm
DETECTOR (10,000 cm2 at a distance of 100 cm)
Detectable fraction
0.08
Efficiency of detector
0.20
Background (B) for given gamma-energy
0.0017/(cm2 s)
TIME TO DETECTION (signal three standard deviations above background, m = 3)
130 minutes
Background values are from S. Fetter et al. and D. Srikrishna et al., op. cit.
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Time to Detection
as a function of the shielding, for clean HEU (12 kg, 7% U-238)
Time to detection [minutes]
200
Time to detection: 130 minutes
Weight of lead-shielding: 164 kg
150
100
50
Time to detection: 17 seconds
Weight of lead-shielding: 62 kg
Time to detection: 6 minutes
Weight of lead-shielding: 105 kg
0
0
2
4
6
8
Thickness of lead-shielding [cm]
10
12
(Detector with an effective area of 10,000 cm2 at 100 cm distance)
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Passive Detection of SNM
12 kg HEU
12 kg HEU
4 kg WPu
(clean, 7% U-238)
(contaminated, 0.00000001% U-232)
(93% Pu-239)
Gamma radiation
84,500/s at 1.001 MeV
321,600/s at 2.615 MeV
937,440/s at 0.769 MeV
Self-shielding of sphere
G = 0.10 for µ = 1.41/cm
G = 0.16 for µ = 0.87/cm
G = 0.10 for µ = 2.08/cm
EXTERNAL SHIELDING (10 cm of lead)
Correction
F = 0.00045 for λ = 0.77/cm
F = 0.00674 for λ = 0.50/cm
F = 0.00004 for λ = 1.01/cm
DETECTOR (10,000 cm2 at a distance of 100 cm)
Detectable fraction
0.08
0.08
0.08
Efficiency of detector
0.20
0.20
0.20
Background
0.0017/(cm2 s)
0.0003/(cm2 s)
0.0073/(cm2 s)
TIME TO DETECTION (signal three standard deviations above background, m = 3)
130 minutes
0.2 seconds
more than 10 hours
Note: plutonium can be passively detected by its neutron emissions
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How Does a γ-Spectrum Look Like?
1989 “Black Sea Experiment” - Soviet SLCM, measurements on launch tube
This is what one would look
for (in the case of clean HEU)
S. Fetter, T. B. Cochran, L. Grodzins, H. L. Lynch, and M. S. Zucker, “Measurements of Gamma Rays from a Soviet Cruise Missile,”
Science, 248, 18 May 1990, pp. 828-834
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GAO’s Assessment
Statement of G. Aloise, 14 March 2007
“ Instead of using the results of its performance tests
conducted in 2005, DNDO’s [cost-benefit] analysis
simply assumed that ASPs could detect highly
enriched uranium 95 percent of the time, a
performance level far exceeding the capabilities of the
new technology’s current demonstrated capabilities.
The 2005 test results showed that the best of the three
winning vendor monitors could only identify masked
HEU* about 50 percent of the time.”
*Masking is an attempt to hide dangerous nuclear or radiological
material by placing it with benign radiological sources
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Active Detection
(briefly)
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“Nuclear Car Wash”
(Livermore Concept)
D. R. Slaughter et al., “Preliminary results utilizing high-energy fission product γ-rays to detect fissionable material in cargo,”
Nuclear Instruments and Methods in Physics Research B, 241 (2005), 777-781
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“Nuclear Car Wash”
(Detection of beta-delayed high-energy gamma-radiation)
100000
Gamma-radiation above 3 MeV [counts]
Sum of two curves
10000
55 s decay
SNM target in
1000
14 MeV pulsed neutron source
illuminates target/cargo-setup for
30 seconds - followed by a 100-second
counting interval (shown here)
100
10
SNM target out
Target/cargo setup: 380 grams of HEU
within plywood (61 cm thickness)
Detector distance: 2 meters
7.1 s decay
1
0
20
40
60
80
100
Time [sec]
D. R. Slaughter et al., “Preliminary results utilizing high-energy fission product γ-rays to detect fissionable material in cargo,”
Nuclear Instruments and Methods in Physics Research B, 241 (2005), 777-781
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Active Methods, cont’d
Active techniques using
pulsed neutron sources or
high-energy gamma-rays
require heavy shielding
and cannot be used with
vehicles carrying passengers
Concept proposed by research group at University of Wisconsin (detection of delayed neutrons)
R. Radel et al., Detection of HEU Using a Pulsed D-D Fusion Source, 2006 Technology of Fusion Energy Conference, 15 November 2006
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Imaging Techniques
“ These X-rays, viewed simultaneously, provide the most information about the
contents of the truck's container. Transmission X-rays penetrate the mixed cargo
providing a “shadowgram” X-ray (top) revealing dark anomalies indicating dense
materials. The detailed Z Backscatter image (bottom) highlights lower density
materials, providing context and clarity to expedite inspection.”
American Science & Engineering, Inc.
www.as-e.com
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Imaging Techniques
American Science & Engineering, Inc.
www.as-e.com
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Imaging Techniques
ZBV (Z Backscatter Van) - Promotional Video
American Science & Engineering, Inc.
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Summary
Passive Detection
Special Nuclear Materials (and in particular highly enriched uranium)
have weak characteristic signatures
Vulnerability to countermeasures (evasion of detection)
Active Detection
More robust than passive techniques
Several concepts under research and development
Intrusiveness may/will raise privacy (and possibly public health) issues
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Summary
Detection Systems in General
Needs uniform detection coverage across every transportation mode
Focused on (and most effective at) points-of-entry
about 650 metric tons of HEU (40% of global inventory) are “already” in the United States
(mostly at military sites or in deployed nuclear weapons - but also at civilian research-reactor sites)
Fixed-detector systems will likely displace
illicit trafficking to means of transport that avoid portals
(for a discussion, see for example D. Srikrishna et al.)
Complementary Approaches to Nuclear Detection
Global cleanout of civilian highly enriched uranium
(conversion of research reactors to low-enriched fuel, shutdown and defueling of unneeded facilities)
More general: no fissile materials in the nuclear fuel cycle
(would include stopping reprocessing of spent fuel, i.e. separation of plutonium)
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References
•
•
•
•
•
S. Fetter, V. A. Frolov, M. Miller, R. Mozley, O. F. Prilutsky, S. N. Rodionov, and R. Z. Sagdeev,
“Detecting Nuclear Warheads,” Science & Global Security, Vol. 1, Nos. 3-4, 1990, pp. 225-253
S. Fetter, T. B. Cochran, L. Grodzins, H. L. Lynch, and M. S. Zucker, “Measurements of Gamma Rays
from a Soviet Cruise Missile,” Science, 248, 18 May 1990, pp. 828-834
D. Srikrishna, A. N. Chari, T. Tisch, “Deterrence of Nuclear Terrorism with Mobile Radiation
Detectors,” The Nonproliferation Review, Volume 12, Number 3, Fall/Winter 2005, pp. 573-614
D. R. Slaughter et al., “Preliminary results utilizing high-energy fission product γ-rays to detect
fissionable material in cargo,” Nuclear Instruments and Methods in Physics Research B, 241 (2005),
pp. 777-781
American Science & Engineering, Inc., www.as-e.com
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