Cargo Scanners Research Articles

Dose estimation in X-ray backscatter imaging with Timepix3 and TLD detectors

Nowadays, the detection of backscatter X-rays has become an essential part of road security scanners, where individuals are at risk of an accidental exposure to the pulsed photon radiation fields generated by the devices that implement this technique. Dose to soft-tissue measurements of a pulsed radiation field generated by a commercial cargo X-ray backscattering device are presented using a Timepix3 detector. To accurately estimate the imparted dose, the energy spectrum of a backscattering cargo scanner is measured with a thick CdZnTe hybrid semiconductor pixel detector. The deconvolution of this measured spectrum is performed and the contributions to the dose are calculated by means of the mass energy-absorption coefficients for soft-tissue. This methodology was assessed through a Monte-Carlo simulation, together with verification measurements using thermoluminescent detectors (TLDs) as a standard dosimetry system. Measurements of direct irradiation, for a 30 s scan with the device at 2 m from the detector, yielded a dose of (4.9 ± 0.7) μGy and (3.6 ± 0.3) μGy for the Timepix3 and TLDs, respectively. In a simulated cargo environment, with the detector behind a 1 mm thick steel wall, 30 s scan time, and 2 m source to detector distance, the dose measured by the Timepix3 was (1.7 ± 0.1) μGy, while for the TLDs (1.4 ± 0.6) μGy, showing that the proposed methodology has a similar response as compared to a standard dosimetry system.

Ir-192 radioisotope replacement with a hand-portable 1 MeV Ku-band electron linear accelerator

Although linear accelerators are used in many security, industrial and medical applications, the existing technologies are too large and expensive for several critical applications such as radioactive source replacement, field radiography and mobile cargo scanners. One of the main requirements for these sources is to be highly portable to allow field operation. In response to this problem, RadiaBeam has designed a hand-portable 1 MeV X-ray source, scalable to higher energies, based on Ku-band split electron linac, that can be used for Ir-192 radioisotope replacement. In this paper, we present its multiphysics and engineering design studies, as well as an accelerating structure prototype along with RF measurements.

Studies on a dual energy RF electron linac

Beam dynamics study of a dual energy (6/3.5 MeV) standing wave RF electron Linac as a cargo scanner is carried out in the code ASTRA . This paper discusses a detailed study on focusing of electron beam aiming to reduce the emittance growth and spot size & presents the solenoid misalignment tolerances. Simulation of X-ray production is performed in FLUKA code.

Reprint of ‘Evaluation of Scattered Radiation Emitted From X-ray Security Scanners on Occupational Dose to Airport Personnel’

Based on security issues and regulations airports are provided with luggage cargo scanners. These scanners utilize ionizing radiation that in principle present health risks toward humans. The study aims to investigate the amount of backscatter produced by passenger luggage and cargo toward airport personnel who are located at different distances from the scanners. To approach our investigation a Thermo Electron Radeye-G probe was used to quantify the backscattered radiation measured in terms of dose-rate emitted from airport scanners, Measurements were taken at the entrance and exit positions of the X-ray tunnel at three different distances (0, 50, and 100cm) for two different scanners; both scanners include shielding curtains that reduce scattered radiation. Correlation was demonstrated using the Pearson coefficient test. Measurements confirmed an inverse relationship between dose rate and distance. An estimated occupational accumulative dose of 0.88mSv/y, and 2.04mSv/y were obtained for personnel working in inspection of carry-on, and cargo, respectively. Findings confirm that the projected dose of security and engineering staff are being well within dose limits.

Creating a reference database of cargo inspection X-ray images using high energy radiographs of cargo mock-ups

Customs continue to use a wide range of technology in protecting against terrorism and the movement of illicit trade and prohibited imports. The throughput of scanned vehicles and cargo increases and just keeps on growing. Therefore, the need of automated algorithms to help screening officers in inspection, examination or surveillance of vehicles and containers is crucial. In this context, the successful collaboration between manufacturers and customs offices is of key importance. Facing this topic, within the seventh framework program of the European Commission, the project ACXIS “Automated Comparison of X-ray Images for cargo Scanning” arose. This project develops a reference database for X-ray images of illegal and legitimate cargo, procedures and algorithms to uniform X-ray images of different cargo scanners, and an automated identification of potentially illegal cargo.

Evaluation of scattered radiation emitted from X-ray security scanners on occupational dose to airport personnel

Based on security issues and regulations airports are provided with luggage cargo scanners. These scanners utilize ionizing radiation that in principle present health risks toward humans. The study aims to investigate the amount of backscatter produced by passenger luggage and cargo toward airport personnel who are located at different distances from the scanners. To approach our investigation a Thermo Electron Radeye-G probe was used to quantify the backscattered radiation measured in terms of dose-rate emitted from airport scanners, Measurements were taken at the entrance and exit positions of the X-ray tunnel at three different distances (0, 50, and 100cm) for two different scanners; both scanners include shielding curtains that reduce scattered radiation. Correlation was demonstrated using the Pearson coefficient test. Measurements confirmed an inverse relationship between dose rate and distance. An estimated occupational accumulative dose of 0.88mSv/y, and 2.04mSv/y were obtained for personnel working in inspection of carry-on, and cargo, respectively. Findings confirm that the projected dose of security and engineering staff are being well within dose limits.

Vertical intensity modulation for improved radiographic penetration and reduced exclusion zone

In the present work, a method to direct the X-ray beam in real time to the desired locations in the cargo to increase penetration and reduce exclusion zone is presented. Cargo scanners employ high energy X-rays to produce radiographic images of the cargo. Most new scanners employ dual-energy to produce, in addition to attenuation maps, atomic number information in order to facilitate the detection of contraband. The electron beam producing the bremsstrahlung X-ray beam is usually directed approximately to the center of the container, concentrating the highest X-ray intensity to that area. Other parts of the container are exposed to lower radiation levels due to the large drop-off of the bremsstrahlung radiation intensity as a function of angle, especially for high energies (>6 MV). This results in lower penetration in these areas, requiring higher power sources that increase the dose and exclusion zone. The capability to modulate the X-ray source intensity on a pulse-by-pulse basis to deliver only as much radiation as required to the cargo has been reported previously. This method is, however, controlled by the most attenuating part of the inspected slice, resulting in excessive radiation to other areas of the cargo. A method to direct a dual-energy beam has been developed to provide a more precisely controlled level of required radiation to highly attenuating areas. The present method is based on steering the dual-energy electron beam using magnetic components on a pulse-to-pulse basis to a fixed location on the X-ray production target, but incident at different angles so as to direct the maximum intensity of the produced bremsstrahlung to the desired locations. The details of the technique and subsystem and simulation results are presented.

Design and development of a focusing electromagnet for RF linac of a cargo scanner

Cargo scanning of contraband objects by high energetic X-rays requires compact and self-contained RF linacs. To achieve this goal, a 6MeV, 700W standing wave RF electron linac has been developed at Accelerator and Pulse Power Division, BARC. To obtain the image of scanned objects with good resolution requires a focused electron beam at the target. This paper presents the design, development and integration of a solenoid magnet with a compact RF linac and its performance with electron beam for cargo scanning applications.

WE‐G‐301‐01: Airport Security Imaging Systems: Design, Dose, Risks, and Quality

Imaging at ports of entry into the United States has become ubiquitous— cargo scanners at seaports; CT luggage scanners, x‐ray backscatter whole‐ body scanners, and millimeter wave imaging systems at airports. The use of x‐ray backscatter scanners has become quite controversial in that hundreds millions to over a billion of people will be exposed to very low levels of radiation, perhaps many times each year, in the U.S. alone.This special symposium has been developed for the medical physics community in order to provide technical information about these scanners and the risk of exposing large numbers of airline staff and passengers, including pregnant women and children, to ionizing or electromagnetic radiation. Since the primary purpose of these systems is to provide a security tool, one must also consider the quality of the images produced and the ability to detect contraband material.

Anti-coincidence rejection of SiPM dark pulses for improved detection of low energy radiation

Neutron and gamma detectors of the CSIRO air cargo scanner are based on scintillators readout by photodiodes (PD). The scanner imaging resolution is limited by the scintillator size. It, in turns, is limited by the number of interactions that can be detected by the PD. Silicon photomultipliers (SiPM) could be used in place of PDs to improve the neutron and gamma detector efficiency. It would ultimately improve the scanner performance in terms of speed, cargo size and image quality. Efficient use of SiPM requires gain stabilisation and dark counts suppression. This work presents a technique to strip the dark counts and the electronic noise off the genuine source-induced spectrum. The method requires the use of a pair of SiPM coupled to the same scintillator. By rejecting the events not detected by both the SiPMs, the background counts were reduced by more than 99%.

Development of a Fast-Neutron Detector With Silicon Photomultiplier Readout

A robust neutron detector was developed to monitor the neutron flux in fast-neutron/gamma radiography (FNGR) cargo scanners. The main features of the new neutron detector were an ability to handle high count rate for statistical precision and a high damage threshold for longevity when used close to intense fast neutron sources (up to 1010 n/s). The detector comprises a fast scintillator coupled to a shielded 100 pixel Hamamatsu 1 mm times 1 mm silicon photomultiplier (SiPM) via a 220 cm length of wavelength shifting (WLS) plastic fibre. The WLS fibre was glued onto two long sides of a 10 times 10 times 50 mm scintillator wrapped in Tyvek reflector. Scintillation pulses of up to ~40 photons reached the SiPM. With the detector mounted 60 mm from a Thermo A-325 DT neutron generator (up to 6 times 107 n/s) the count rate was over 4 times 104 counts per second. The SiPM gain was effectively stabilised against temperature variations by automatically trimming the bias voltage with SiPM temperature. Comparison data is provided for a photodiode-scintillator neutron detector placed 134 cm from the A-325 neutron generator and for a PMT-WLS-scintillator neutron detector.

Determination of ambient and personal dose equivalent for personnel and cargo security screening

In the past few years, imaging technology using ionising radiation has been gaining in importance for the screening of goods and persons for security reasons and in order to detect contraband. For radiation protection purposes it is extremely important to know that dose persons are exposed to when passing through a personnel scanner or, as a stowaway, in a cargo scanner, so as to remain within the prescribed dose limits. Within the scope of a research project, measurements were performed on different types of personnel X-ray scanners as well as cargo X-ray scanners, using the transmission and/or the backscattering method. All scanners investigated operate with a high dose rate and use short irradiation time. Owing to this method of scanning reliable values can only be determined for the personal and ambient dose equivalents, H(p)(10) and H(*)(10), by using a specially developed measuring system. The aim of this project was to determine the range of magnitudes of doses for representative personnel and cargo X-ray scanner systems. Depending on the type of scanner, the determined dose values for personnel scanners range from 0.07 microSv to 6 microSv. Measurements and instruments used in this study are described and the dose values obtained are discussed in detail.