NONDESTRUCTIVE IDENTIFICATION OF
CHEMICAL WARFARE AGENTS
AND EXPLOSIVES BY NEUTRON
GENERATOR-DRIVEN PGNAA
T. R. TWOMEY a, A.J. CAFFREY b, and D. L.
CHICHESTER b
a
ORTEC Division, Ametek, Inc., Oak Ridge, Tennessee 37831 USA
b
Idaho National Laboratory, Idaho Falls, Idaho 83415 USA
1
Abstract
•PGNAA is now a proven method for the identification of
chemical warfare agents and explosives in military projectiles
and storage containers.
•Idaho National Laboratory is developing a next-generation
PGNAA instrument based on the new Ortec Detective
mechanically-cooled HPGe detector and a neutron
generator.
•Agenda
–Review PGNAA analysis of suspect chemical
warfare munitions
–Advantages and disadvantages of Cf-252 neutron
source vs compact accelerator neutron generator.
2
1.1 The “Non-Stockpile” Munitions Identification Problem
Clear Markings of a French World War I-era
mustard gas 75-mm artillery projectile.
3
A typical “Non-Stockpile” Munition
No Markings or identification. 4.7-inch artillery projectile found in the
Spring Valley neighborhood of Washington, D.C., January 1993.
PGNAA determined this “non-stockpile” projectile contains an incendiary chemical.
The projectile was likely buried in 1919.
4
1.2. Prompt Gamma-ray Neutron Activation
Analysis (PGNAA) solution
• Neutrons excite atomic nuclei
within munition
• Nuclei de-excite, emitting
characteristic gamma rays
• Gamma-ray signature reveals
chemical elements inside
• Fill compound or mixture inferred
from elements detected
• Advantage is that both neutrons
and gamma rays are penetrating
5
Safe and lawful non-stockpile disposal requires
• Fill Chemicals:
identification
• Explosives
• Smoke generating agents
– Titanium Tetracholride
– White Phosphorus
• CW agents
– Blister agents
– Chocking Agents
– Nerve gases
– Other CW agents
• Training Munitions
• Sand
• Concrete
• Water/Antifreeze
• Plaster-of- Paris
Clear Vision • Sound Strategies • Solid Performance
6
Portable Isotopic Neutron Spectroscopy
(PINS) chemical assay System 1991.
• First PGNAA system designed for
identification of chemical warfare
agents.
• A commercial product of the
ORTEC Division of Ametek,
Inc.since 1995.
• Thousands of suspect chemical
non-stockpile munitions in
worldwide, since 1992.
• Calibrated on most types of
military explosives and every type
of chemical munition in the
current U.S. stockpile
7
PINS Design Requirements
• Reduce or eliminate direct sampling
– Treaty verification
– Old and abandoned munitions & containers
– Counterterrorism
• Classify munition & container fills
–
–
–
–
Chemical warfare (CW) agents
Explosives
Smoke chemicals (e.g. White phosphorus [WP])
Practice fills (e.g. sand, water)
• User friendly
– Hand-portable and rugged
– Operable by non-experts
– In-situ analysis results
8
1st and 2nd Generation PINS use Cf-252 and
LN2-cooled HPGe
• HPGe spectroscopy system
essential to separate fill
chemical signal from
background from the munition
body.
– e.g. 155-mm artillery projectile
filled with sarin (GB) nerve
agent, fill chemical mass ~3 kg,
total mass ~, 41 kg.
PINS-2 MCA
9
1.3 Neutron generator-based PGNAA
instruments for munition fill identification
• INL has begun design of 3rd
generation PINS to simplify
operation:
– Modified ORTEC Detective
– Neutron Generator
• Eliminate LN2 Hazard and
inconvenience: more rugged
Potential for other uses (RadNuc)
• Eliminate Source Hazard and
transport problems
10
Ortec Detective
• High-resolution HPGe detector
• Mechanically cooled (No LN2)
• Built-in multichannel analyzer,
HVPS
• Power:
30 watts, 3-hour battery
life
– 110-220 VAC,
– 12-volt DC
• Cool-down time:
4-6 hours
– same as LN2-cooling
11
Portable and Small
• Size: 12.5” L, 6.3” W, 13.1” H (~ 50-cal ammunition box)
• Weight: 22 pounds (10 kg)
• All-attitude: needn’t sit level to operate correctly
12
The ORTEC Detective/trans-SPEC cutaway
•LN2-free Stirling cooler
• >50,000 hrs continuous
operation
•“clearance seal technology”
13
Mixed-Source Gamma-Ray Spectrum
14
Electrical neutron generators
•
INL has evaluated neutron generators
from
– Activation Technology Corp.
– All-Russia Institute of Automatics (VNIIA)
– EADS/SODERN
– Thermo Electron
•
Also performing R&D with an INL
research project (LDRD) for advanced
neutron generators
– Examining plasma physics & ion dynamics
in Penning ion sources
– Partnering with LBNL to explore suitability
of RF ion source technology for active
interrogation
SODERN Genie-16 neutron generator with
(overpacked) chemical warfare munition
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2. PGNAA FOR CW AGENTS AND
EXPLOSIVES
2.1 Response of atomic nuclei to neutrons
• Elemental ratios only: Technique is
•
•
not sensitive to chemical bonding.
For munitions, limited number of
chemical types, allows fill chemical
inference
Gamma-ray energies and intensities
for dexcitation gamma ray spectra
are known and catalogued for all
naturally occuring elements in
periodic table
16
2.2 Elemental composition of CW agents, explosives, and
military smokes
Hydrogen
Carbon
Oxygen
Nitrogen
Fluorine
Phosphorus
Sulfur
Chlorine
Arsenic
Sarin
(GB)
7.1
34.3
22.9
13.6
22.1
Soman
(GD)
8.8
46.2
17.6
17.3
10.4
17.0
Tabun
(GA)
6.8
37.0
19.8
5.2
19.1
VX
9.7
49.4
12.0
11.6
12.0
Mustard
(HD)
5.0
30.2
20.1
44.7
Lewisite
(L)
1.0
11.4
51.3
36.1
• Nerve agents GA, GB, GD, and VX are organophosphorus
•
•
•
compounds.
VX can be distinguished from the G series of nerve agents by the
presence of sulfur.
Blister agents mustard and lewisite contain no phosphorus, but
both contain about 45-50 weight-% chlorine
Lewisite can be distinguished from mustard agent by the absence
of sulfur and the presence of arsenic.
17
HD vs. HE
18
GB and HD Spectra
19
Military explosives
Hydrogen
Carbon
Oxygen
Nitrogen
Fluorine
Phosphorus
Sulfur
Chlorine
Arsenic
Comp. B
2.5
24.5
42.8
30.4
HMX
2.7
16.2
43.2
37.8
PETN
2.5
19.0
60.8
17.7
RDX
2.7
16.2
43.2
37.8
Tetryl
1.7
29.0
44.6
24.4
TNT
2.2
37.0
42.3
18.5
• Most explosives contain a few weight-% hydrogen, about 20-40
weight-% nitrogen, approximately 40-60 weight-% oxygen, and a
balance of carbon.
20
Military obscuring smokes
FM
Hydrogen
Carbon
Oxygen
Aluminum
Titanium
Phosphorus
Sulfur
Chlorine
Zinc
•
•
•
•
FS
0.4
51.5
HC
WP
4.7
9.2
6.7
25.3
100.0
74.7
34.4
13.7
41.9
37.5
FM smoke: Titanium tetrachloride,;
FS smoke: chlorosulfonic acid and sulfur trioxide;
HC smoke: aluminum, hexachloroethane, and zinc oxide
WP smoke: white phosphorus.
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2.3 PINS System munition fill id decision tree
• Analyzes 8,192-channel gamma-ray spectra. Executes decision tree
algorithm every ten seconds, presents assay results in real time.
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PINS Graphical User Interface
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3. NEUTRON GENERATOR VS. Cf-252 EXCITATION FOR PGNAA
Parameter
Neutron Yield, n/s
Neutron Spectrum
Pulsing Range, Hz
Power Consumption, W
Mass, kg
General Size, cm
2 mrem/hr stand-off distance, m
252
Cf (10 µg)
8
0.23 x 10
Watt Fission Spectrum
Continuous only
0
0.01
0.01 x ∅ 0.01
3.5
Neutron Generator
8
2 x 10
14.1 ± 0.1 MeV
Continuous up to 20,000
50
12
16 x 60 x 30
13.8
• Cf-252 half-life 2.645 years.
• Specific neutron emission rate 2.314 x106 n s-1µg-1
• Used in PINS system for >15 years.
Compact accelerator neutron generators
• higher neutron emission intensity.
• harder neutron spectrum
• Can be turned-off when not in use.
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3.1. Advantages: logistics, safety, higher output, background
issues
Higher energy neutrons from a DT source
• Allow excitation of higher energy nuclear inelastic scattering
reactions which are non-existent or very weak when interrogating
using fission spectrum neutrons.
– help to improve precision and speed in the analytical determination of some CW
agents and in identifying non-CW fill materials.
(Includes explosive identification based upon oxygen analysis.)
Practical advantages
• Can be turned off or into stand-by mode.
– Easy placement of objects
– Easy shipment
•
•
•
•
Higher Neutron yield (10x c.f. 10µG Cf-252)
Lack of associated gamma rays, c.f. Fission souce
Lifetimes now several 000’s hrs continuous operation.
Pulsed operation
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3.2. NG Disadvantages: detector shielding problem, background
issues
•
Size, complexity, and power requirements.
– (not that much larger or heavier then 252Cf in its 20 kg radiation shielding/shipping container).
•
May need to use an external assembly to attempt to boost the thermal neutron
intensity within the test object,
•
Larger outer diameter of neutron generators means larger/heavier external
moderator assemblies in standard PINS: usually require several kilograms of
material.
•
•
Neutron generator often requires the use of a control computer. (Small issue)
Electrical power required
•
More Shadow Shielding Required
– Standard PINS 10 cm of tungsten and 1cm of Bi protect HPGe detector from fission neutrons and
photons.
– High yield DT NG 20-30cm tungsten and or other high Z materials needed to ensure fast n flux will
not damage HPGe and introduce dead-time to PGNAA electronics.
•
More Complex PGNAA Spectra
– High energy DT fusion neutrons interact with nearby structural and background material: more
reaction channels.
– HPGe resolution is adequate to deal with this.
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3.3. Neutron generator reliability concerns
• Radioisotope sources are 100% reliable, even if inconvenient.
•
24/7 365 days/year not needed for PINS:
– 3000 seconds per object.
– 12 objects/day
•
Early neutron generators lasted a few hundred hours and failures were
unpredictable, and often catastrophic.
•
More recent systems (<10years) failure mode is a slow degradation in output: more
manageable
– Rapid transition from stand-by to full output (30-45 seconds, previously up to 10 minutes)
– Even with significant target erosion and loss of yied, a PINS NG should last several years.
Ruggedness
•
Modern commercial neutron generators are still sensitive electronic instruments and
must be handled carefully.
– Far from meeting typical MILSPEC for shock and vibration, electronics enclosures do not typically
meet criteria such as the NEMA 4 standard.
– However PINS systems with HPGe detectors in use by field technicians and military personnel
around the world under extreme conditions of temperature, humidity, and blowing sand.
Tougher is always Better!
27
Comparison of PINS Instruments by Version
parameter
Standard PINS
miniPINS
PINS-3
ID Capabilities
CW agents, explosives,
smoke, inert fills
CW agents, explosives,
smoke, inert fills
CW agents, explosives,
smoke, inert fills,
radionuclides
ID Limitations
bio agents, radionuclides
bio agents, radionuclides
bio agents
Downrange weight
96 pounds
46 pounds
30-40 pounds
Shipping weight
409 pounds
192 pounds
60-70 pounds
Power
15 watts
5 watts
35 watts
Power source
110-220 VAC ,
internal battery,
or 12 VDC source
110-220 VAC ,
internal battery,
or 12 VDC source
110-220 VAC ,
internal battery,
or 12 VDC source
LN2 consumption
2 liters/day
2 liters/day
n/a--mechanically cooled
Battery life
8 hours
8 hours
3 hours
Detector
HPGe
HPGe
HPGe
MCA type
Analog
Digital
Digital
Neutron source
Cf-252 source
Cf-252 source
neutron generator
Acquisition/analysis
sequential
concurrent
concurrent
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Summary of Next Generation PINS
• New mechanically-cooled HPGe detector
– High resolution
– No liquid nitrogen required
• Neutron generator in lieu of Cf-252 source
– Improved radiation safety
• Improved identification of chemical warfare materiel &
explosives
• New software for extending the chemical library
– Toxic industrial chemicals
– Radionuclide identification
29
Acknowledgments
• R&D funding
– Defense Threat Reduction Agency
– U.S. Army PM/Non-Stockpile Chemical Materiel
– U.S. Department of Energy
• R&D colleagues & collaborators
– INL: John Baker, Larry Blackwood, Ann Egger, Steve Frickey, Ken Krebs,
Cathy Riddle, Ed Seabury, Jayson Wharton, John Zabriskie
– Ortec: Rusty Bingham, Benson Davis, Ron Keyser, T.J. Paulus, Pat
Sansingkeow, Dan Upp
30