Cargo inspection by means of electromagnetic radiation

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Cargo inspection by means of

electromagnetic radiation

Master’s thesis

Author: Muhammad Shakeel Arshad Supervisor: Sven-Erik Sandström Examiner: Sven-Erik Sandström Term: VT21

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Acknowledgments

I would like to show my gratitude to Prof. Sven-Erik Sandström for his support. He never

hesitated in giving me any kind of help and always showered me with advice. He showed me

a lot of tolerance, comprehension, and encouragement during the progress of this study.

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List of Figures

Figure 1 Inspection of cargo. ... 2

Figure 2 Electromagnetic frequency bands. ... 3

Figure 3 Schematics of Compton scattering. ... 5

Figure 4 Mobile inspection unit. ... 6

Figure 5 Full scale cargo inspection... 7

Figure 6 Cargo inspection by means of X-rays. ... 8

Figure 7 X-ray cargo inspection method for a truck. ... 9

Figure 8 Electromagnetic Scanner (EMIS) 6047 and 8075... 10

Figure 9 X-ray vehicle scanner. ... 11

Figure 10 X-ray scanner mechanism using shielding curtains. ... 12

Figure 11 C-BORD project and user perspective. ... 13

Figure 12 C-BORD framework perspectives. ... 14

Figure 13 Baggage X-ray units for cargo inspection. ... 15

Figure 14 Identified AFIs of baggage X-ray units. ... 16

Figure 15 The cargo inspection facility. ... 18

Figure 16 NQR detection schematically. ... 19

Figure 17 Blighter surveillance systems ... 20

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Abstract

This study is based on a detailed literature review of the approaches that are being used for inspecting cargos. It was concluded that especially X-rays are suitable for precise inspection of cargos due to high-quality output images. The images captured with X-Ray scanning methods are sufficient for discriminating various materials. Methods for the inspection of cargos with the help of electromagnetic radiation at radio frequencies are also discussed.

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Chapter 01 Introduction

Cargo inspection is the method of inspection of goods and items in the transportation system. The increasing volumes of goods and the risk of terrorist attacks motivates cargo inspection. The scope of the research in this field is expanding and new methods are being developed. From a physics point of view, the methods of inspection are electromagnetic [30].

Scanning techniques are based on X-rays and radio frequency techniques. The aim here is to discuss new uses of very high frequencies in the case of X-rays. X-rays are electromagnetic waves with a very high frequency. The range of frequency for X-rays is from 30 PetaHertz to 30 ExaHertz. Some important RF techniques are [7]:

 Nuclear Quadrupole Resonance  Doppler Radar

 Switched-Antenna-Array Radar Imaging

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The inspection mostly deals with objects on trucks and particularly the inspection of Intermodal freight shipping containers. Intermodal freight is a mode of transportation through big containers that contain raw materials and various products. Containers are transported by different modes: ships, trains, aircraft and trucks. The scope is illustrated by the involvement of the Department of Homeland Security. The subdepartment known as the Container Security Initiative (CSI) had the goal of inspecting all cargos by 2012.

The extended cargo inspection was recommended by the US Congress and the 9/11 Commission. The main aim of cargo scanning in the US is to detect various sorts of Special Nuclear Materials (SNMs), but also other suspicious cargo. The form for cargo inspection in other countries is different and oriented towards verification. Cargo inspection simplifies tariff collection and identification of contraband. Research shows that more than eighty percent of the cargos in the US was inspected in February 2009 [13].

Radiation at low frequency, used in radar for instance, could be used to detect hidden objects due to the capacity for penetration. Older techniques for this are less precise. The devices are categorized as passive or active [25].

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Scope of the research

There is evidence that there is an increase in terrorism and drug trafficking worldwide, aided by various modes of transport. Cargo is also used for the transportation of various explosives. Explosives, terrorism and drugs form a complex.

Explosives were used in major terrorist attacks from 2001 to 2010, such as the Moscow Metro bombing and the Nevsky Express bombing. The protection of the travelers is a key objective of the cargo system. Cargo inspection detects hidden objects and provides help and support. The research is focusing on new methods for cargo inspection as well as improving existing methods.

Background to the study

The material of the cargo determines the methods of inspection. Inspection could be made with X-rays or radio frequency waves. X-rays can easily penetrate metallic as well as nonmetallic materials.

This indicates that X-ray inspection is the most suitable form of cargo inspection for most materials. Radio Frequency (RF) techniques are normally used for nonmetallic materials. For metals like silver and aluminum, the incident frequency must be higher than the plasma frequency of that particular material. Waves that have higher frequencies can pass through these metals. For metallic cargo there is the problem of reflection. For non-metallic cargo like plastic and wood there is no such problem [6].

Compton scattering

X-ray cargo inspection is based on the concept of backscattering of waves. In Compton scattering there is a reduction of the energy in the returned wave. If a wave is transmitted towards a target, the change in wavelength is given by the formula:

𝜆_𝑓− 𝜆_𝑖 =ℎ(1 − cos 𝜃) 𝑚𝑒𝑐

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The formula describes an increase in wavelength that can be observed due to interaction between the wave photons and free electrons. The scattering is in all directions, indicated by the angle θ. The change in wavelength is zero at θ=0. Scatter imaging resembles natural imaging, where the eye constructs an image from the reflected light from the surface of all objects. Radiation could penetrate deeply into the object and enables volume imaging and hence a detailed inspection of the cargo. The entities involved are [21]:

Figure 3 Schematics of Compton scattering [9].

𝜆_𝑓 The wavelength after scattering

𝜆_𝑖 The incident wavelength

h The Planck constant

c The speed of light

𝑚𝑒 The electron mass at rest

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Previous research in the field

Various methods are being used for inspection, but electromagnetic techniques are comparatively mobile and deployable. The proposed methods are capable of scanning various cargos in a cost-effective and accurate way. Many of the proposed methods also work for uneven surfaces.

The proposed portable method is based on image representation. The radiation source is mobile and combined with a detector array. The source of radiation is connected to the boom (12) in Fig. 4.

Figure 4 Mobile inspection unit [20].

The principle is referred to as digital radiography which is a method for non-destructive testing. With this approach, the radiation image of the object under test is recorded in digital form. The received data are stored digitally in the computer memory. This technique is now common and well-studied [20].

Objectives of the research

The main objectives for this study are:

1. To define the cargo inspection concept.

2. To identify and review the methods that are being used for cargo inspection.

3. To understand and discuss the principles of electromagnetic scattering for the detection of objects.

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Chapter 02 Literature review

The study deals mainly with X-ray inspection. The identification of materials is the most important task of an effective system [30].

Various technologies have evolved for cargo inspection. Research has introduced inspection based on X-rays and neutrons. Studies indicate that mono-energetic X-rays gives good material identification. X-ray sources operate on the principle of RF electron linear acceleration (linacs). Researchers are focusing on the concept of neutron imaging and neutron analysis for cargo inspection. In addition, there is nuclear resonance fluorescence and computer tomography.

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Methods of X-ray detection

X-ray are electromagnetic waves with a very high frequency, ranging from 30 PetaHertz to 30 ExaHertz. Consequently, X-ray photons have a very high energy ranging from 100 electron volts to 100 keV. One method for cargo inspection is based on the Compton backscattering effect.

Figure 6 Cargo inspection by means of X-rays [31].

X-ray inspection necessitates the emission of a beam that is directed towards the target. The scattered X-rays are collected by means of detectors [18].

The amount of material is measured by means of the atomic number for that material. The scanning is achieved by moving either target or detector so as to create a 2D image. This reflection method is applicable if just one side of the cargo is available. X-ray detection can differentiate various types of materials.

To identify the materials, the intensity of the scattered rays is linked to the atomic number of the material. Organic materials seem brighter in the final images due to the lower atomic numbers. This could be used to identify and categorize materials as organics or non-organics. This indicates that X-ray backscatter imaging could be used for the detection of explosive materials [27].

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Figure 7 X-ray cargo inspection method for a truck [3].

In addition, various types of drugs and weapons could be identified by observing transmitted fields. In this case the image is produced with the help of X-rays that are transmitted through the target. The X-ray images indicate that darker sections of the image represent low penetration while lighter sections represent high penetration [29].

Neutron imaging is yet another suitable technique. Recent research describes inspection by means of nuclear resonance fluorescence. Computer tomography [21] is another suitable method and so is the use of dual-energy X-rays.

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An electromagnetic inspection scanner (EMIS) automatically detects the dangerous objects inside books, bags, and other organic materials. It is fast and the most efficient method of non-metallic inspection The EM scanner operates at frequencies from 10 to 100 MHz. The EMIS 6047 and 8075 are used for the scanning of packages and is shown in Fig. 8 [16].

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Advantages of electromagnetic cargo inspection

Some advantages of EM radiation that are discussed in the literature.

 Methods that operate on EM radiation are fully automatic and provide accurate detection.

 EM radiation can identify initiators and metal components that are present in various explosive devices.

 EM radiation is suitable for perishable goods as well as organic products generally.  The intensity of EM radiation is low [13].

 EM radiation provides complete data logging and helps in traceability [18].

X-ray scanning is typically used to examine luggage and parcels that are being taken or loaded on vehicles. The inspection is normally carried out when the cargo container enters buildings. The drive-through portal (DTP) 7.5 MeV X-ray scanner [2] is used for the inspection of containers and appears in Fig. 9. The scanner is simple, and allows a continuous flow of luggage. Penetrating X-rays produce images of the items in the container [31].

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The key feature of the X-ray scanning mechanism is that the shapes and sizes of the objects are detected by a single scanning system. The radiation is enclosed within the system by means of shielding curtains. The curtains are placed at the entry and exit of the X-ray scanning system. The shielding has a laminated design and is made of lead vinyl. Lead rubber and Teflon combined with other ingredients are also used to form a thin sheet of shielding material [31].

The materials of the curtain are configured in such a manner that they block electromagnetic radiation. The shielding curtains are composed of flap portions that are made up of polymer and other material that is spread uniformly.

The emitted radiation is blocked at the entry and exit of the X-ray scanner system. The shielding curtains are designed and manufactured in laminated form. The layers of the shielding curtains are also made of lead vinyl. The thin sheets of the containers (Item 18 in Fig. 10) are also made of lead rubber along with teflon. The curtain strips are designed so that the thickness of the curtain is even and independent of the surface texture. Fig. 10 shows the mechanism of the X-ray scanner including the shielding curtains mounted in bars (Item 30,31).

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There are many advantages with these curtains. One is the mounting features that are directly molded on the curtain. The important advantage here is easy installation and easy removal. Molded curtains also permit the molding of the texture of the shielding curtain. The suggested design reduces the coefficient of friction and can also reduce the area of the curtain that interacts with the parcel. The items can then pass through the inspection system more easily [30].

Another important advantage with this system is the elimination of lead since the curtains are made of composite polymer material. The important benefit of using polymers is that they are more flexible than conventional materials and thus reduce the friction. The result is an increased throughput of goods. The number of points where the cargos have to stop for inspection are significantly reduced.

Figure 11 C-BORD project and user perspective [10].

The report includes an overview of the non-destructive techniques in the cargo system. It indicates that various well-adapted methods could be efficient. It also includes the design of the C-BORD project that is an effective method frequently used for cargo inspection at border control points.

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The work on the C-BORD project was started in the year 2015 and it was implemented in 2020. The report includes an overview of the latest developments in that area. Previous work served as the basis for the C-BORD project. The research was funded by the European Union FP6 and FP7 calls. Researchers worked on the issues of EURITRACK and UNCOSS as well as the SNIFFER and SCINTILLA project [12].

Figure 12 C-BORD framework perspectives [10].

The report gives a detailed overview of the main goals of the C-BORD project. Researchers focused on finding technical solutions with emphasis on the detection of non-radiological threats. The researchers have found many important facts by extensive research on detection of explosives and evaporation-based cargo inspection. Research on rapidly relocatable tagged neutron inspection systems (RRTNIS) was made and various aspects of the technology has been pursued. Various studies are conducted on the detection of radiological hazardous materials. Researchers have focused on nuclear threats and the advanced radiation portal monitors (RPM) [28].

The impact on the human body has also been investigated regarding hazardous effects on drivers and other people [4].

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Figure 13 Baggage X-ray units for cargo inspection [4].

The Australian radiation protection and nuclear safety agency (ARPANSA) has acted on this and inspected baggage or packed X-ray units in the period June 2016 to July 2017. Both cargo, diplomatic post, and passengers at international airports were inspected. An ARPANSA report disclosed various areas for improvement (AFI). The inspection was based on regulatory priority (RP), where RP indicated the level of risk associated with the object under inspection. RP1 was tagged to items of the highest priority and RP6 to those with the lowest priority [4].

The report summarized that people that are licensed, and are dealing with baggage X-ray units, need to present a compliance report twice a year only. An ARPANSA report describes the inspected X-ray cabinets according to the radiation health series (RHS) 21 and the generation of X-rays in a shielded container [4].

The Radiation health series 21 is related to shielding and external radiation. Radiation health series 21 also deals with the safety and maintenance of X-ray generation [31]. RHS 21 also deals with the concept of item examination access and the control of initiating and terminating the X-ray generation. The Radiation health series 21 provides guidelines regarding lighting, signage, and monitoring of X-ray units. The organizations that work according to series 21 say that there is only a small amount of radiation that is not dangerous to human health.

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Figure 14 Identified AFIs of baggage X-ray units [4].

Most nations have passed laws according to which it is necessary to scan the cargo. United States legislation requires scanning for intermodal cargo containers that are received at a US airport. This law was passed in 2013. The inspection is accomplished with accelerator-driven high-energy X-rays. The energy of the X-rays is between 4 to 9 MeV and this range is effective for scanning operations [10].

For the future, the productivity of the systems needs to be improved. The objective is to reduce the costs of acquisition and operation. Maintenance of the cargo system requires the assurance that the driver can pass the irradiation area safely [15].

It requires that the driver can pass through the controlled area where they are exposed to a high-energy beam. Research shows that there is little danger if the drivers are exposed briefly. They are only exposed to the scattered beam and the direct beam is avoided. This has been investigated by means of Monte-Carlo simulations. The present statistics includes the case of failure of the safety system and accidental exposure to a direct beam.

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Chapter 03 Methodology

The cargo inspection facility is a room that consists of an accelerator and an additional irradiation area that is known as the inspection tunnel. It is shielded with ordinary concrete walls. The shielding walls have sufficient thickness so as to reduce the dose rate in the nearby areas. As for the standards, the dose in nearby areas must be less than 0.5 µSv/h. The process of inspection is performed by driving the truck through the irradiation area. The required fixed speed in this process is 1 m/s [15].

The accelerator unit runs at an energy suitable for inspection. The machine releases an X-ray beam of 4.5, 6, or 9 MeV. In the conventional process, the angle of release of the vertical X-ray beam is fixed to 48°. The reason for this angle is that it could cover the entire cargo container. The angle of the horizontal X-ray is fixed to 1.5°. The reason for this angle is the creation of a fan-shaped beam. The fan-shaped beam minimises the spread and enhances the image quality [15]. The front view of the machine appears in Fig. 15.

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Cargo inspection methods using electromagnetic radiation

X-ray inspection

X-rays are categorized as electromagnetic waves with very high frequencies. The range of frequency for X-rays is from 30 petahertz to 30 exahertz. The energy of an X-ray is between 100 electron volts to 100 KeV. The conventional method for cargo inspection is Compton backscattering [25].

As discussed earlier, the inspection is based on the atomic number and can separate organics or non-organics [4]. The X-rays scan the materials irrespective of their position. There are also methods that operate at radio frequencies.

Nuclear Quadrupole Resonance (NQR)

This method of cargo inspection uses radio frequencies (RFs) in non-metallic containers for the detection of explosive materials. In addition, nuclear quadrupole resonance could be used for the detection of specific drugs. The fundamental principle is that scattered waves are created in the interaction between the RF wave and the quadrupole moment of the nucleus [23].

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The material is exposed to the electric field gradient. The excited RF wave is transmitted toward the decided target, which results in a change in the frequency of the nuclear quadrupole. Each type of molecule has a unique frequency related to the electric field gradient. This process also includes a reemission of the RF wave according to the nature of the material. This reemission allows the identification of specific materials. The method is most suitable for moderate frequencies. It is suitable for the detection of explosive materials and various drugs [23].

Doppler radar systems

The fundamental process is the Doppler effect. The Doppler effect is important since it provides information about the velocity of the target. The Doppler effect gives a shift in the frequency of the received signal. This approach is used to detect the motion of the target. Doppler radar systems are used in the band 0.3 to 12.5 GHz [13].

The frequency is chosen so that it could penetrate cargos that have nonmetallic bodies. The Doppler effect is used to detect minor movements like the slow breathing or the heartbeat of a person. The method is suitable for cluttered situations with objects near the antenna.

The unique capability for detecting movement makes it possible to find concealed stowaways. A drawback is that the system is sensitive to noise [13].

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Switched-Antenna-Array radar imaging system

A Switched-Antenna phased array radar is an effective system for inspection. The S-band frequencies are in the range of 1.9 to 4 GHz and the modulation method is frequency-modulated continuous wave (FMCW). The main feature of the system is that it sends and receives the signal at the same time. This waveform is used when waves need to pass a dielectric obstacle of small width. An implementation is shown in Fig. 18 [8].

Figure 18 Switched-Antenna-Array [26].

The range of the radar is between 0 and 20 meters. An advantage of this system is that it can eliminate the air-slab reflections that reduce the radar sensitivity. The design includes the radar imaging system and it is appropriate for imaging concealed targets at a short range.

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Chapter 04 Conclusion

This study covers the methods that are being used for cargo inspections. The first conclusion is that X-rays are suited to precise inspection with the help of high-quality output images. The images that are captured by the X-ray scanning make it possible to discriminate different materials. Various procedures used for the cargo inspection by means of electromagnetic radiation are described. A notable limitation is that low frequencies cannot be used for metallic bodies. Refrigerator trucks could not be inspected by low-frequency radiation for this reason. It was observed that low-frequency detection is appropriate for dielectric bodies such as flatbed trucks.

It is concluded that X-ray inspection is the most suitable form of cargo inspection since X-rays can easily penetrate both metallic and nonmetallic materials. X-ray cargo inspection uses backscattering in the form of Compton scattering where the scattered wave has a reduced energy. The points of inspection are normally seaports and airports. Cargo inspection is important as a means to achieve the intentions of homeland security, such as the control of nuclear materials. New technologies involve concepts like dual-energy X-rays and neutron radiation. X-ray sources work on the principle of RF electron linear accelerators (linacs).

It is concluded that the technique of electromagnetic radiation provides more mobile and rapidly deployable inspection. There are also methods that work for uneven surfaces. There are various portable inspection systems for cargos that create an image representation of the cargo. Digital Radiography Systems is a method of performing non-destructive radiation testing. It is observed that organic materials seem brighter in the final images because they have lower atomic numbers.

Neutron imaging is another efficient technique for cargo inspection. Electromagnetic radiation can also be used with nuclear fluorescence resonance technology. Cargo inspection methods that operate with electromagnetic radiation are fully automatic and provide accurate detection. In summary it is clear that cargo inspection is an active research area.

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Cargo inspection by means of electromagnetic radiation