- Email: [email protected]
Classifying threats with a 14-MeV neutron interrogation system
ARTICLE IN PRESS
Applied Radiation and Isotopes 63 (2005) 799–803 www.elsevier.com/locate/apradiso
Classifying threats with a 14-MeV neutron interrogation system Dan Strellis, Tsahi Gozani Ancore Corporation, 2950 Patrick Henry Drive, Santa Clara, CA 95054, USA
Abstract SeaPODDS (Sea Portable Drug Detection System) is a non-intrusive tool for detecting concealed threats in hidden compartments of maritime vessels. This system consists of an electronic neutron generator, a gamma-ray detector, a data acquisition computer, and a laptop computer user-interface [Strellis et al., 2003, Proceedings of the 2003 ONDCP International Technology Symposium, San Diego, CA]. Although initially developed to detect narcotics, recent algorithm developments have shown that the system is capable of correctly classifying a threat into one of four distinct categories: narcotic, explosive, chemical weapon, or radiological dispersion device (RDD). Detection of narcotics, explosives, and chemical weapons is based on gamma-ray signatures unique to the chemical elements. Elements are identified by their characteristic prompt gamma-rays induced by fast and thermal neutrons. Detection of RDD is accomplished by detecting gamma-rays emitted by common radioisotopes and nuclear reactor fission products. The algorithm phenomenology for classifying threats into the proper categories is presented here. r 2005 Elsevier Ltd. All rights reserved. Keywords: Neutron generator; 14-MeV neutron; Thermal neutron analysis; Fast neutron analysis; Neutron activation; Explosive detection; Chemical weapons detection; Drug detection; Dirty bomb
1. Introduction Sea Portable Drug Detection System (SeaPODDS) was developed to detect narcotics concealed in hidden compartments onboard fishing vessels. Since the September 11 tragedy, detecting additional bulk threats has become a high priority to authorities securing our borders. To counter the added threat, new algorithms were added to the SeaPODDS capability. SeaPODDS will now detect a wide variety of targets including
Corresponding author. Tel.: +408 727 0607; fax: 408 727 8748. E-mail address: [email protected] (D. Strellis).
narcotics, explosives, chemical weapons, and nuclear materials. Detecting threats behind hidden compartments onboard marine vessels requires the system to be manportable, rugged, water resistant, and user friendly (see Fig. 1). The sensor must be able to probe through thick walls and provide an automatic decision in a relatively short period of time. These requirements can be reasonably well met by using an appropriate configuration of a neutron source, neutron spectrum tailoring, gamma-ray detector type, and shielding material. The underlying technology uses both TNAs (thermal neutron analysis) and FNATM (fast neutron analysis). These technologies measure, in a complementary way, elemental (hence material) specific signatures. Usability
0969-8043/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.apradiso.2005.05.037
ARTICLE IN PRESS 800
D. Strellis, T. Gozani / Applied Radiation and Isotopes 63 (2005) 799–803
is further enhanced by automatically classifying the inspection as benign or suspect. If suspect, then the algorithm further classifies the suspect as an explosive, narcotic, chemical weapon, or RDD. Knowing the nature of the threat allows the inspector to take appropriate action to clear the suspected area.
Fig. 1. Rendering of SeaPODDS inspecting a hidden cavity.
2. Material signatures Nuclear techniques detect the presence of materials of interest by detecting signatures of specific nuclei through their unique nuclear structures. Narcotics, explosives, and chemical weapons are unique and different from most benign materials because of their elemental compositions (Gozani, 1981, 1991; Gozani et al., 1989; Vourvopoulos et al., 1991; Bendahan et al., 1999) as shown in Table 1. Table 1 clearly shows that a narcotic like cocaine hydrochloride can be efficiently measured with TNA using a combination of H and Cl features. Combining TNA with FNA to measure C and/or O will further enhance the measurement. Explosives can be efficiently measured with TNA using the N and H features. Combining TNA with FNA to measure oxygen will further enhance the measurement. Chemical weapons have inherently different signatures because they vary greatly in elemental composition. Nerve agents, blister agents, and blood agents contain chemicals that are designed to attack very
Table 1 Elemental composition of common substances, narcotics, explosives, and chemical weapons Substance
Density (g/cm3)
%H
%C
%N
Benigns Salt Sugar Sand Water Wood Petroleum Cement PVC Polyethylene Fiberglass Sea water
0.77 1.2 2.3 1 0.62 0.87 2.3 1.32 0.94 1.7 1.02
Explosives PETN TNT Dynamite C4
1.76 1.63 1.18 1.65
2.4 2.2 4.2 3.6
19 37 14.8 21.9
17.7 18.5 18.5 34.4
0.87 0.87 0.87 0.87
6 6.5 6.3 6.9
62.1 60.1 68.2 67.3
3.7 5 7.1
44.5 30.2 34.3
Narcotics Heroin hydrochloride Cocaine hydrochloride Heroin Cocaine Chemical_weapons Hydrogen cyanide Mustard gas Sarin
0 7 0 11 6 14 0 5 14 3 10
0 42 0 0 47 86 0 38 86 46 0
0 0 0 0 0 0 0 0 0 0 0
%O
0 51 53 89 44 0 35 0 0 35 88
%Cl
% Other elements
Examples of elemental siqnatures C/O
N/O
Cl/C
Cl/H
0 0 0 0 0 0 0 11.5 0 0 0.03
60 0 0 0 0 0 0 57 0 0 1.2
40 0 47 0 3 0 65 0 0 16 0.8
0 0.8 0 0 1.1 0 0 0 0 3 0
0 0 0 0 0 0 0 0 0 1.3 0
0 0 0 0 0 0 0 1.5 0 0 0
60.8 42.3 62.4 40.1
0 0 0 0
0 0 0 0
0.3 0.9 0.2 0.6
0.3 0.4 0.3 0.9
0 0 0 0
0 0 0 0
3.5 4.1 3.8 4.6
19.7 18.8 21.7 21.1
8.7 10.4 0 0
0 0 0 0
3.2 3.2 3.2 3.2
0.2 0.2 0.2 0.2
0.1 0.2 0 0
1.5 1.6 0 0
51.8 0 0
0 0 22.9
0 44.6 0
0 20.2 35.7
0 0 1.5
0 0 0
0 1.5 0
0 8.9 0
ARTICLE IN PRESS D. Strellis, T. Gozani / Applied Radiation and Isotopes 63 (2005) 799–803
different parts of the human body. Nerve agents such as VX and Sarin inhibit acetylcholinesterase throughout the body. Since the normal function of this enzyme is to hydrolyze acetylcholine wherever it is released, such inhibition results in the accumulation of excessive concentrations of acetylcholine at its various sites of action. These sites include parasympathetic nerves. Nerve agents tend to have large amounts of phosphorus and fluorine. Blister agents attack the skin, mucous membranes, lungs, and blood-forming organs. One of the most feared blister agents, sulfur mustard, contains about 45% chlorine by weight. Blood agents prevent tissue cells from using oxygen. As a result, organs quickly stop working. Hydrogen cyanide is an example of a blood agent. It contains about 50% nitrogen by weight. Because chemical weapons contain elements common to narcotics (Cl) and explosives (N), secondary features must be used to classify them correctly. Using combinations of TNA, FNA, and Boolean logic, they can be properly classified. RDD threats (a.k.a. ‘‘dirty bombs’’) emit gamma-rays by way of their natural radioactive decay. Neutron interrogation is not necessary for their detection. Both TNA and FNA are used by SeaPODDS to gather the wealth of information available to the system. The system uses this information to offer a powerful tool to the user—the ability to detect and classify threats into four unique categories (explosive, drugs, chemical weapons, and RDD).
3. SeaPODDS technology TNA is based on characteristic gamma-rays generated by the capture of thermal neutrons by most elements; paramount among them are hydrogen, nitrogen and chlorine. This forms the basis of detection of explosives and drugs and certain chemical agents. FNA is based on characteristic gamma-rays generated by the inelastic scattering of fast neutrons (e.g. 14 MeV) on most elements; principally among them are carbon and oxygen. Using a nuclear-based technique as a tool in searches of boarded maritime vessels demands weight and size limitations. Only a switchable neutron source, electronic neutron generator (ENG), is feasible for this application. Such a source can be switched off and requires much less personnel shielding than a system utilizing a radioisotope neutron source. ENGs have been used for decades in borehole logging for oil and other applications. An ENG generates neutrons by accelerating deuterons through a high voltage (HV), typically 75–100 kV onto a tritium target. The resulting deuterium–tritium reaction creates 14-MeV neutrons. When the HV is off, no neutrons are produced. Under this
801
Fig. 2. FNA and TNA spectra of a hidden compartment containing cocaine simulant.
condition it is completely safe to move the generator and other system modules to another location for inspection. Many commercially available ENGs can be operated in a pulsed mode. Under this setting, 14-MeV neutrons are produced only during short pulses, 5 ms or wider, with repetition rates of 10–10,000 pulses per second. During the pulse all the prompt fast neutron interactions take place. After the pulse, only the fast neutrons that were slowed down and thermalized in the surrounding environment exist. Their population decays with time constants of the order of tenths to a few milliseconds. During this time only thermal neutron interactions take place. The quality of the resulting thermal gamma-ray spectrum is particularly good due to the complete absence of fast neutron interactions with the object and the gamma-ray detector. The presence of these interactions would cause degradation in the thermal spectrum. Since neutrons thermalize within a couple hundred nanoseconds after being generated and others survive from the previous pulse, some thermal capture reactions will always occur during the neutron pulse. Thus the fast spectrum is always somewhat contaminated with gamma-rays from thermal capture reactions. However, the true FNA spectrum can be successfully extracted, thus extending and enhancing TNA’s capability to detect drugs. This technique to correct the fast spectrum has been utilized in SeaPODDS (Gozani et al., 2001). The two sets of spectra shown in Fig. 2 show the wealth of elemental information. The complementary nature of the spectra collected during the neutron pulse (FNA) and between the pulses (TNA) proves useful for contraband detection.
4. Algorithm development The TNA and FNA spectral features form the basis for detection. The SeaPODDS threat detection algorithms use key spectral features to separate benign materials from threats. The general detection algorithms are based on weighting the key features to arrive at the
ARTICLE IN PRESS 802
D. Strellis, T. Gozani / Applied Radiation and Isotopes 63 (2005) 799–803
Fig. 3. A 2-feature plot showing separation of explosives/HCN and other materials. The dashed lines indicate the boundaries of the threat field. The arrows point to the threat field.
Fig. 4. A 2-feature plot showing separation between HCN and explosives. The dashed line is the boundary. HCN alarms lie above the line. Explosive alarms lie below the line.
best separation between benign materials and threats. The classification algorithms utilize secondary filtering to separate the four threat types. In general, the algorithms were derived after performing a suite of measurements under many different conditions. For instance, samples of different types (both threats and benign materials) were placed behind a compartment wall. The compartment wall material was composed of materials commonly found onboard fishing vessels. The wall thickness and the sample standoff distances were also varied. The thermal and fast spectra were analyzed for spectral features that differentiate known threats with known benign materials. Classifying the threat into the correct threat category is a challenge for threats in different categories having the same primary key features. For instance, hydrogen cyanide and explosives have nitrogen as its primary key feature. Table 1 shows clearly that these two threats have large N compositions. These two threats can be separated from other materials by utilizing this primary feature as shown in Fig. 3. For these cases, a separate algorithm was developed from secondary spectral features to separate the two threats with the same primary features. In Fig. 4, separation is demonstrated by plotting the explosive algorithm vs. the secondary filter algorithm. Similar algorithm developments were undertaken for the other threat types.
lying TNA and FNA technologies can decode the bulk elemental composition of the contents of hidden compartments through neutron interrogation. Highly developed threat detection and classification algorithms provide a strong indication as to the type of threat detected. If a threat is suspected, the system automatically categorizes the threat as a narcotic, explosive, chemical weapon, or RDD. This automatic decision prevents user misinterpretation, thus reducing false alarms and missed detections. The classification feature allows the operator to make the appropriate response based on the threat type suspected.
5. Conclusions SeaPODDS has the potential to become a powerful tool for material specific non-intrusive inspection. The design of the system components and the packaging has focused on usability and man-portability. The under-
Acknowledgments The authors would like to express their appreciation to the following for their support and continued interest in the program: Ms. Elisabeth D’Andrea, Mr. Butch Burgess and Dr. Steven Haimbach of NSWC, Mr. Doug Murray of NTMI, Mr. Eric Helm of the US Coast Guard, and Mr. Tom Cassidy of Sensor Concepts and Applications Inc.
References Bendahan, J., et al., 1999. Mobile drug detection system for the inspection of vehicles and cargo containers. Proceedings of the 1999 ONDCP International Technology Symposium, Washington, DC. Gozani, T., 1981. Active Nondestructive Assay of Nuclear Materials—Principles and Applications. NUREG/CR0602, Chapter 9. Gozani, T., 1991. In: Khan, S.M. (Ed.), Proceedings of First International Symposium on Explosive Detection Techno logy, Atlantic City, NJ, DOT/FAA/CT-92/11, pp. 27–55.
ARTICLE IN PRESS D. Strellis, T. Gozani / Applied Radiation and Isotopes 63 (2005) 799–803 Gozani, T., Seher, C.C., Morgado, R.E., 1989. Nuclear based explosive techniques—1989 status. Proceedings of the Third International Symposium on Analysis and Detection of Explosives, Manheim, Germany. Gozani, T., et al., 2001. SeaVEDS—Nonintrusive inspection of maritime vessels for concealed drugs, Proceedings of the 2001 ONDCP International Technology Symposium, San Diego, CA.
803
Strellis, D., Gozani, D., Chivers, D., 2003. SeaPODDS—A material specific man-portable drug detection system. Proceedings of the 2003 ONDCP International Technology Symposium, San Diego, CA. Vourvopoulos, G., et al., 1991. A pulsed fast thermal neutron interrogation system. In: Khan, S.M. (Ed.), Proceedings of First International Symposium on Explosive Detection Technology, Atlantic City, NJ. DOT/FAA/CT-92/11, pp. 104–115.
Applied Radiation and Isotopes 63 (2005) 799–803 www.elsevier.com/locate/apradiso
Classifying threats with a 14-MeV neutron interrogation system Dan Strellis, Tsahi Gozani Ancore Corporation, 2950 Patrick Henry Drive, Santa Clara, CA 95054, USA
Abstract SeaPODDS (Sea Portable Drug Detection System) is a non-intrusive tool for detecting concealed threats in hidden compartments of maritime vessels. This system consists of an electronic neutron generator, a gamma-ray detector, a data acquisition computer, and a laptop computer user-interface [Strellis et al., 2003, Proceedings of the 2003 ONDCP International Technology Symposium, San Diego, CA]. Although initially developed to detect narcotics, recent algorithm developments have shown that the system is capable of correctly classifying a threat into one of four distinct categories: narcotic, explosive, chemical weapon, or radiological dispersion device (RDD). Detection of narcotics, explosives, and chemical weapons is based on gamma-ray signatures unique to the chemical elements. Elements are identified by their characteristic prompt gamma-rays induced by fast and thermal neutrons. Detection of RDD is accomplished by detecting gamma-rays emitted by common radioisotopes and nuclear reactor fission products. The algorithm phenomenology for classifying threats into the proper categories is presented here. r 2005 Elsevier Ltd. All rights reserved. Keywords: Neutron generator; 14-MeV neutron; Thermal neutron analysis; Fast neutron analysis; Neutron activation; Explosive detection; Chemical weapons detection; Drug detection; Dirty bomb
1. Introduction Sea Portable Drug Detection System (SeaPODDS) was developed to detect narcotics concealed in hidden compartments onboard fishing vessels. Since the September 11 tragedy, detecting additional bulk threats has become a high priority to authorities securing our borders. To counter the added threat, new algorithms were added to the SeaPODDS capability. SeaPODDS will now detect a wide variety of targets including
Corresponding author. Tel.: +408 727 0607; fax: 408 727 8748. E-mail address: [email protected] (D. Strellis).
narcotics, explosives, chemical weapons, and nuclear materials. Detecting threats behind hidden compartments onboard marine vessels requires the system to be manportable, rugged, water resistant, and user friendly (see Fig. 1). The sensor must be able to probe through thick walls and provide an automatic decision in a relatively short period of time. These requirements can be reasonably well met by using an appropriate configuration of a neutron source, neutron spectrum tailoring, gamma-ray detector type, and shielding material. The underlying technology uses both TNAs (thermal neutron analysis) and FNATM (fast neutron analysis). These technologies measure, in a complementary way, elemental (hence material) specific signatures. Usability
0969-8043/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.apradiso.2005.05.037
ARTICLE IN PRESS 800
D. Strellis, T. Gozani / Applied Radiation and Isotopes 63 (2005) 799–803
is further enhanced by automatically classifying the inspection as benign or suspect. If suspect, then the algorithm further classifies the suspect as an explosive, narcotic, chemical weapon, or RDD. Knowing the nature of the threat allows the inspector to take appropriate action to clear the suspected area.
Fig. 1. Rendering of SeaPODDS inspecting a hidden cavity.
2. Material signatures Nuclear techniques detect the presence of materials of interest by detecting signatures of specific nuclei through their unique nuclear structures. Narcotics, explosives, and chemical weapons are unique and different from most benign materials because of their elemental compositions (Gozani, 1981, 1991; Gozani et al., 1989; Vourvopoulos et al., 1991; Bendahan et al., 1999) as shown in Table 1. Table 1 clearly shows that a narcotic like cocaine hydrochloride can be efficiently measured with TNA using a combination of H and Cl features. Combining TNA with FNA to measure C and/or O will further enhance the measurement. Explosives can be efficiently measured with TNA using the N and H features. Combining TNA with FNA to measure oxygen will further enhance the measurement. Chemical weapons have inherently different signatures because they vary greatly in elemental composition. Nerve agents, blister agents, and blood agents contain chemicals that are designed to attack very
Table 1 Elemental composition of common substances, narcotics, explosives, and chemical weapons Substance
Density (g/cm3)
%H
%C
%N
Benigns Salt Sugar Sand Water Wood Petroleum Cement PVC Polyethylene Fiberglass Sea water
0.77 1.2 2.3 1 0.62 0.87 2.3 1.32 0.94 1.7 1.02
Explosives PETN TNT Dynamite C4
1.76 1.63 1.18 1.65
2.4 2.2 4.2 3.6
19 37 14.8 21.9
17.7 18.5 18.5 34.4
0.87 0.87 0.87 0.87
6 6.5 6.3 6.9
62.1 60.1 68.2 67.3
3.7 5 7.1
44.5 30.2 34.3
Narcotics Heroin hydrochloride Cocaine hydrochloride Heroin Cocaine Chemical_weapons Hydrogen cyanide Mustard gas Sarin
0 7 0 11 6 14 0 5 14 3 10
0 42 0 0 47 86 0 38 86 46 0
0 0 0 0 0 0 0 0 0 0 0
%O
0 51 53 89 44 0 35 0 0 35 88
%Cl
% Other elements
Examples of elemental siqnatures C/O
N/O
Cl/C
Cl/H
0 0 0 0 0 0 0 11.5 0 0 0.03
60 0 0 0 0 0 0 57 0 0 1.2
40 0 47 0 3 0 65 0 0 16 0.8
0 0.8 0 0 1.1 0 0 0 0 3 0
0 0 0 0 0 0 0 0 0 1.3 0
0 0 0 0 0 0 0 1.5 0 0 0
60.8 42.3 62.4 40.1
0 0 0 0
0 0 0 0
0.3 0.9 0.2 0.6
0.3 0.4 0.3 0.9
0 0 0 0
0 0 0 0
3.5 4.1 3.8 4.6
19.7 18.8 21.7 21.1
8.7 10.4 0 0
0 0 0 0
3.2 3.2 3.2 3.2
0.2 0.2 0.2 0.2
0.1 0.2 0 0
1.5 1.6 0 0
51.8 0 0
0 0 22.9
0 44.6 0
0 20.2 35.7
0 0 1.5
0 0 0
0 1.5 0
0 8.9 0
ARTICLE IN PRESS D. Strellis, T. Gozani / Applied Radiation and Isotopes 63 (2005) 799–803
different parts of the human body. Nerve agents such as VX and Sarin inhibit acetylcholinesterase throughout the body. Since the normal function of this enzyme is to hydrolyze acetylcholine wherever it is released, such inhibition results in the accumulation of excessive concentrations of acetylcholine at its various sites of action. These sites include parasympathetic nerves. Nerve agents tend to have large amounts of phosphorus and fluorine. Blister agents attack the skin, mucous membranes, lungs, and blood-forming organs. One of the most feared blister agents, sulfur mustard, contains about 45% chlorine by weight. Blood agents prevent tissue cells from using oxygen. As a result, organs quickly stop working. Hydrogen cyanide is an example of a blood agent. It contains about 50% nitrogen by weight. Because chemical weapons contain elements common to narcotics (Cl) and explosives (N), secondary features must be used to classify them correctly. Using combinations of TNA, FNA, and Boolean logic, they can be properly classified. RDD threats (a.k.a. ‘‘dirty bombs’’) emit gamma-rays by way of their natural radioactive decay. Neutron interrogation is not necessary for their detection. Both TNA and FNA are used by SeaPODDS to gather the wealth of information available to the system. The system uses this information to offer a powerful tool to the user—the ability to detect and classify threats into four unique categories (explosive, drugs, chemical weapons, and RDD).
3. SeaPODDS technology TNA is based on characteristic gamma-rays generated by the capture of thermal neutrons by most elements; paramount among them are hydrogen, nitrogen and chlorine. This forms the basis of detection of explosives and drugs and certain chemical agents. FNA is based on characteristic gamma-rays generated by the inelastic scattering of fast neutrons (e.g. 14 MeV) on most elements; principally among them are carbon and oxygen. Using a nuclear-based technique as a tool in searches of boarded maritime vessels demands weight and size limitations. Only a switchable neutron source, electronic neutron generator (ENG), is feasible for this application. Such a source can be switched off and requires much less personnel shielding than a system utilizing a radioisotope neutron source. ENGs have been used for decades in borehole logging for oil and other applications. An ENG generates neutrons by accelerating deuterons through a high voltage (HV), typically 75–100 kV onto a tritium target. The resulting deuterium–tritium reaction creates 14-MeV neutrons. When the HV is off, no neutrons are produced. Under this
801
Fig. 2. FNA and TNA spectra of a hidden compartment containing cocaine simulant.
condition it is completely safe to move the generator and other system modules to another location for inspection. Many commercially available ENGs can be operated in a pulsed mode. Under this setting, 14-MeV neutrons are produced only during short pulses, 5 ms or wider, with repetition rates of 10–10,000 pulses per second. During the pulse all the prompt fast neutron interactions take place. After the pulse, only the fast neutrons that were slowed down and thermalized in the surrounding environment exist. Their population decays with time constants of the order of tenths to a few milliseconds. During this time only thermal neutron interactions take place. The quality of the resulting thermal gamma-ray spectrum is particularly good due to the complete absence of fast neutron interactions with the object and the gamma-ray detector. The presence of these interactions would cause degradation in the thermal spectrum. Since neutrons thermalize within a couple hundred nanoseconds after being generated and others survive from the previous pulse, some thermal capture reactions will always occur during the neutron pulse. Thus the fast spectrum is always somewhat contaminated with gamma-rays from thermal capture reactions. However, the true FNA spectrum can be successfully extracted, thus extending and enhancing TNA’s capability to detect drugs. This technique to correct the fast spectrum has been utilized in SeaPODDS (Gozani et al., 2001). The two sets of spectra shown in Fig. 2 show the wealth of elemental information. The complementary nature of the spectra collected during the neutron pulse (FNA) and between the pulses (TNA) proves useful for contraband detection.
4. Algorithm development The TNA and FNA spectral features form the basis for detection. The SeaPODDS threat detection algorithms use key spectral features to separate benign materials from threats. The general detection algorithms are based on weighting the key features to arrive at the
ARTICLE IN PRESS 802
D. Strellis, T. Gozani / Applied Radiation and Isotopes 63 (2005) 799–803
Fig. 3. A 2-feature plot showing separation of explosives/HCN and other materials. The dashed lines indicate the boundaries of the threat field. The arrows point to the threat field.
Fig. 4. A 2-feature plot showing separation between HCN and explosives. The dashed line is the boundary. HCN alarms lie above the line. Explosive alarms lie below the line.
best separation between benign materials and threats. The classification algorithms utilize secondary filtering to separate the four threat types. In general, the algorithms were derived after performing a suite of measurements under many different conditions. For instance, samples of different types (both threats and benign materials) were placed behind a compartment wall. The compartment wall material was composed of materials commonly found onboard fishing vessels. The wall thickness and the sample standoff distances were also varied. The thermal and fast spectra were analyzed for spectral features that differentiate known threats with known benign materials. Classifying the threat into the correct threat category is a challenge for threats in different categories having the same primary key features. For instance, hydrogen cyanide and explosives have nitrogen as its primary key feature. Table 1 shows clearly that these two threats have large N compositions. These two threats can be separated from other materials by utilizing this primary feature as shown in Fig. 3. For these cases, a separate algorithm was developed from secondary spectral features to separate the two threats with the same primary features. In Fig. 4, separation is demonstrated by plotting the explosive algorithm vs. the secondary filter algorithm. Similar algorithm developments were undertaken for the other threat types.
lying TNA and FNA technologies can decode the bulk elemental composition of the contents of hidden compartments through neutron interrogation. Highly developed threat detection and classification algorithms provide a strong indication as to the type of threat detected. If a threat is suspected, the system automatically categorizes the threat as a narcotic, explosive, chemical weapon, or RDD. This automatic decision prevents user misinterpretation, thus reducing false alarms and missed detections. The classification feature allows the operator to make the appropriate response based on the threat type suspected.
5. Conclusions SeaPODDS has the potential to become a powerful tool for material specific non-intrusive inspection. The design of the system components and the packaging has focused on usability and man-portability. The under-
Acknowledgments The authors would like to express their appreciation to the following for their support and continued interest in the program: Ms. Elisabeth D’Andrea, Mr. Butch Burgess and Dr. Steven Haimbach of NSWC, Mr. Doug Murray of NTMI, Mr. Eric Helm of the US Coast Guard, and Mr. Tom Cassidy of Sensor Concepts and Applications Inc.
References Bendahan, J., et al., 1999. Mobile drug detection system for the inspection of vehicles and cargo containers. Proceedings of the 1999 ONDCP International Technology Symposium, Washington, DC. Gozani, T., 1981. Active Nondestructive Assay of Nuclear Materials—Principles and Applications. NUREG/CR0602, Chapter 9. Gozani, T., 1991. In: Khan, S.M. (Ed.), Proceedings of First International Symposium on Explosive Detection Techno logy, Atlantic City, NJ, DOT/FAA/CT-92/11, pp. 27–55.
ARTICLE IN PRESS D. Strellis, T. Gozani / Applied Radiation and Isotopes 63 (2005) 799–803 Gozani, T., Seher, C.C., Morgado, R.E., 1989. Nuclear based explosive techniques—1989 status. Proceedings of the Third International Symposium on Analysis and Detection of Explosives, Manheim, Germany. Gozani, T., et al., 2001. SeaVEDS—Nonintrusive inspection of maritime vessels for concealed drugs, Proceedings of the 2001 ONDCP International Technology Symposium, San Diego, CA.
803
Strellis, D., Gozani, D., Chivers, D., 2003. SeaPODDS—A material specific man-portable drug detection system. Proceedings of the 2003 ONDCP International Technology Symposium, San Diego, CA. Vourvopoulos, G., et al., 1991. A pulsed fast thermal neutron interrogation system. In: Khan, S.M. (Ed.), Proceedings of First International Symposium on Explosive Detection Technology, Atlantic City, NJ. DOT/FAA/CT-92/11, pp. 104–115.