Available online at www.sciencedirect.com
ScienceDirect Physics Procedia 90 (2017) 115 – 125
Conference on the Application of Accelerators in Research and Industry, CAARI 2016, 30 October – 4 November 2016, Ft. Worth, TX, USA
Electron Accelerators for Novel Cargo Inspection Methods S. Kutsaev, R. Agustsson, A. Arodzero, S. Boucher*, J. Hartzell, A. Murokh, F. O’Shea, A.Yu. Smirnov RadiaBeam Technologies, LLC, 1717 Stewart St., Santa Monica, CA, 90404, USA
Abstract One of the main factors limiting the performance of conventional x-ray cargo inspection with material discrimination (MD) is the interlaced mode of system operation. Such systems use pulsed linac or betatron x-ray generators and produce alternate bremsstrahlung pulses with lower- and higher- end-point energies. Consequently, these systems provide about 50 mm lower penetration than a system operated in a non-interlaced mode, have a limited range of cargo areal densities with valid MD, and cannot perform MD of objects smaller than the pulse separation. Also, the limited pulse repetition rate of x-ray generators in interlaced mode limits the radiographic image quality at nominal commercial speeds of vehicles or trains. Several new methods of cargo inspection with MD were recently introduced to address the above-mentioned limitations: dualenergy methods based on Scintillation-Cherenkov detectors [1]; multi-energy method based on intrapulse time-varying of spectral content of x-ray [1, 2]; multi-energy method utilized ramping-up energy packet of short x-ray pulses [3, 4]; and methods based on multi-energy betatron [5, 6]. All of these methods have electron accelerators as a core element. However, the accelerator requirements and, thus, their designs, are different for each system. In this paper, we will discuss the requirements for the accelerators, provide some details about their designs, and present several novel solutions for current and future projects. © 2017 2017 Published The Authors. Published Elsevier B.V.access article under the CC BY-NC-ND license by Elsevier B.V.by This is an open (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Scientific Committee of the Conference on the Application of Accelerators in Research Peer-review under responsibility of the Scientific Committee of the Conference on the Application of Accelerators in Research and Industry Industry. and Keywords: Cargo inspection, radiography, material discrimination, electron accelerator, linac, betatron, ramping energy, homeland security.
* Corresponding author. Tel.: +1-310-822-5845, fax: 1-310-582-1212. E-mail address:
[email protected]
1875-3892 © 2017 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Scientific Committee of the Conference on the Application of Accelerators in Research and Industry doi:10.1016/j.phpro.2017.09.036
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Introduction Modern cargo inspection systems can be divided into three types according to their applications: railroad, stationary portal and mobile systems. The security market requirements for x-ray imaging performance of these systems include contrast sensitivity better than 4%, penetration greater than 400 mm of steel equivalent, line pair resolution better than 3.5 mm, 3 Z-groups of MD (organic, inorganic, high Z) over a range of thicknesses up to 200 mm, low dose and small radiation exclusion zone. Conventional dual-energy interlaced cargo inspection systems are lacking the ability to scan cargo at high speeds, precluding efficient x-ray scanning of, for example, railroad cargo for illicit materials such as explosives, drugs and special nuclear materials with minimal interference with the stream of commerce. They demonstrate lower penetration than single energy systems, provide MD only at low speed, and inefficiently utilize x-ray power. They cannot perform Z-discrimination for objects smaller than pulse separation. The maximum penetration is only achieved with the high energy pulse. Finally, these systems have a limited range of areal densities with valid MD due to fixed values of lower and higher interlaced pulse energies. To relieve the aforesaid limitations, RadiaBeam Technologies, LLC is developing several pilot systems that implement the novel inspection methods: x Adaptive Railroad Cargo Inspection System (ARCIS) [4]. This system is based on a multi-energy method utilized a ramping-up energy packet of short x-ray pulses [3], and utilizes a ramped energy source of packets of short (~400 ns) x-ray pulses, a new type of fast X-ray detectors, and rapid processing of detector signals for intelligent control of the linac. The system will allow scanning with MD for speeds up to 45 km/h. x Mobile Intelligent X-ray Inspection System (MIXI) [7]. MIXI relies on a similar concept as ARCIS, but utilizes a compact linac-based X-Ray source, which allows MIXI to be placed on a lightweight truck chassis. x Inspection system with Miniaturized High Energy X-ray Source (MXS). MXS is a compact, high repetition rate linac-based X-ray source that can generate short (~100 ns) pulses with energies up to 9 MeV. The MD algorithm is based on temporal separation of the Scintillation and Cherenkov signals [1]. x Multi-Energy Betatron-based Cargo Inspection System (MEBCIS) [5, 6] relies on an innovative technique of extracting two X-ray pulses with lower and higher energies within a single betatron acceleration cycle. The multi-energy betatron in conjunction with fast X-ray Scintillation-Cherenkov detector will allow a very compact inspection system with intelligent MD. All of the above-mentioned systems have electron accelerators as a core element. However, the accelerator requirements and, thus, their designs are different for each system. The particular requirements for each system type are summarized in Table 1. Table 1. Core parameters of accelerators for novel inspection systems under development at RadiaBeam Technologies (prospective parameters are specified in brackets). System Name
System Type
Beam energy range, MeV
Power source
Pulse repetition rate, pps
Pulse/packet duration, μs
Anticipated average dose per raster line, cGy
Ramping 2-9
Klystron
1,000
16
0.125
Ramping 4 - 6 (2 - 6)
Magnetron (Amplitron)
400
4 (8)
0.055
ARCIS
Railroad
MIXI
Portal, mobile
MXS
Mobile
4/6 (6/9)
Magnetron
500 (2,000)
0.5 (0.1)
0.028
Bx-CIS
Backscatter; mobile, portal
Ramping 0.5 - 1.5
Magnetron (Amplitron)
400 (4,000)
4 (8)
-
MEBCIS
Mobile
Multi-energy 2 - 7.5
Betatron
500
4
0.018
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Accelerators for Inspection Systems In the following sub-sections, we will discuss the requirements of the accelerators for each system, as well as our design approach to reach these parameters. ARCIS: Adaptive Railroad Cargo Inspection System In state-of-the-art interrogation systems, MD is achieved with alternating pulses of high and low energy from the linac [10]. Since each pulse is separated by > 1 ms, overlap of the two energies in the same image slice is not achieved in fast moving cargo [3, 4]. The cargo itself is severely under-sampled at high scan speeds due to small detector element sizes and low x-ray duty factor. Finally, the two fixed end-point energies are best suited for a limited range of cargo areal densities and provide poor performance in other density ranges. In the novel ARCIS technique, each pulse has a range of energies that can be individually detected and analyzed to perform MD. The energy range is adaptive based on the areal density of each region of cargo. This allows increased range of MD, and greatly decreases the total dose per scan. The ARCIS concept is based on the production of packets of short (about 400 ns) x-ray pulses, separated by a 100 ns gap, with ramping-up energy. Depending on the cargo load, it is possible to choose the optimal energy range for MD. For example, if the container is lightly loaded, the energy ramp should be stopped at lower energies. On the contrary, if the container is heavily loaded, the ramp can continue up to 9 MeV. The energy range of each pulse is defined by the information from the previous pulse, and is thus adaptive. Thanks to utilization of this novel adaptive technique, the ARCIS system parameters by far exceed those of conventional interlaced energy systems (see Table 2). To achieve these parameters, a new S-band traveling wave linac with a wide range of energy control has been designed. Table 2. ARCIS parameters compared to conventional system. Conventional 6/9 MeV
ARCIS
Maximum scanning speed with MD, km/h
System parameters
15
45
MD range of thickness, mm of steel equivalent
45-200
6-250
3
4
330
>425
4
1.5
1.0
0.8
Number of Z-groups of MD Penetration, mm of steel Contrast sensitivity at 45 km/h (with 200 mm of steel test object), % Wire detection in air, mm of Cu Wire detection at 45 km/h, mm of Cu
5
