X-ray television installations.

X-ray television installations.

X-ray television installations

The fight against terrorism is impossible without equipping the relevant services with effective technical means for remote detection of weapons and explosive devices (ED) hidden in various objects. This review describes the latest achievements in the field of explosive detection tools using X-ray radiation.

The highest achievements in the development and equipping of technical means for detecting explosives are associated with the solution of aviation security issues. When ensuring security in other areas, technical means created for organizing aviation security are traditionally used directly or with minor modifications.

The task of searching for explosives has arisen almost since the creation of the explosives themselves and consisted mainly of searching for metal casings of explosive devices in the form of mines. At present, the situation has become much more complicated: terrorists have begun to widely use plastic explosives, the detection of which is an incredibly complex technical problem. In this case, we are talking about C-4, used by the US armed forces, or Semtex, which was produced in Czechoslovakia until 1989 and entered the world market in fairly large quantities, as well as Detasheet, produced in the form of 0.25 inch thick sheets. It, in turn, is a third more powerful than trinitrotoluene (TNT), which is twice as destructive as the well-known dynamite. Moreover, Semtex is a favorite among explosives included in the arsenal of professional terrorists. It is believed that the bomb that killed passengers on Pan Am Flight 103 in 1988 was made from this explosive, and its charge was certainly less than one pound (about 450 g).

In addition, further improvements and miniaturization of fuses have made plastic explosives an even more formidable weapon. The fuses themselves are now no larger than the eraser on the end of a pencil. Miniaturization has led to the fact that timers and barometric fuses can be easily hidden from detection. Thus, research into the causes of the above-mentioned airliner crash indicates that in all likelihood the fuse of the bomb placed in the cassette recorder was hidden in the lock of the suitcase, which made it difficult to detect using X-rays.

The set of indicators that a modern X-ray television installation must satisfy and on which the efficiency of its use depends is reduced to the following requirements: — technical, determined by the range of detected explosives by charge mass (no more than 300 g), the probability of correct detection (more than 95%) and the probability of false alarms (less than 5%); — operational, determined by the simplicity and reliability of the installation operation, its adequate throughput (i.e. the time spent on checking one unit of baggage), zero or minimal operator interpretation, the ability to record and store data, transportability and harmlessness to service personnel and air passengers' baggage; — cost, depending on capital investments in production and maintenance costs of the installation.

The effectiveness of X-ray methods for detecting explosives is based on the small difference in density between explosives and substances used in everyday objects with similar atomic numbers. Most of the most common explosives have a density greater than 1.4 g/cm».

This is more than those materials that can be found in controlled household items, such as polyethylene, plastics, leather, etc., not to mention things made of wool and artificial fibers. Only a few of them — with a low atomic number, for example — melanin are close in density to BB. They are rare.

Thus, by simultaneously recording the distribution of density and average atomic number in the controlled baggage, it is possible to detect the presence of hidden explosives with a sufficiently low level of false alarms. As a consequence, X-ray television installations equipped with appropriate hardware and software for processing information contained in transmitted or backscattered X-ray radiation are currently considered the fastest and cheapest (cost effective) means of detecting explosives. Progress in their development in recent years has been the most impressive, and the main direction is the creation of devices capable of detecting explosives without operator intervention.

The world leaders in this area are the American companies EG&G Astrophysics Research Corp., American Science & Engineering Inc., Imatron Inc. and Vivid Technologies Inc., the German company Heimann, the French company Schiumberger Industries, the American company Rapiscan Security Products and the Israeli company Magal Security Systems Ltd. They use different approaches to solving the problem of detecting explosives using X-ray radiation. For example, the company Magal Security Systems Ltcf. focuses on developing installations with the additional ability to automate the process of detecting explosives based on the automatic detection of not the explosives themselves, but the fuses indicating the presence of explosives. The AISYS 370B installation of this company is successfully used in a number of international airports (in combination with other installations), although testing by the Federal Aviation Administration (FAA) did not yield the desired results (the probability of detecting fuses, depending on the category, does not exceed 1-47% with a false alarm of 20%).

A distinctive feature of modern X-ray explosive detection systems is that they use the principle of recording X-ray radiation in two areas of the energy spectrum (dual energy X-ray transmission system).

It was first used by EG&G Astrophysics Research Corp. in a series of installations with the E-Scan option. This option allows one to distinguish organic and inorganic materials in the image of the controlled object (luggage) by their average atomic number. Any object with an atomic number greater than 20 is considered inorganic and is displayed on the monitor screen in blue. Objects with an atomic number less than 10 are considered organic and their image is colored in orange-brown tones, and mixed objects and objects with an atomic number from 10 to 20 are displayed by superimposing blue and orange colors, and finally, objects whose atomic number cannot be determined (for example, the system does not have sufficient penetrating power to transilluminate the object) are displayed in green. Similar options are present in the systems of Heimann, Rapiscan and Schiumberger. However, unlike E-Scan, they use a four-color format, i.e. objects with an atomic number from 10 to 20 and mixed ones containing organics and inorganics are displayed in a separate color. This difference is due to the different distribution of bits of image elements, i.e. 16 bits of an image element are divided between contrast and the number of material classes. Thus, in EG&G Astrophysics systems there are significantly more material classes (32), but the contrast is somewhat lower, and in the other above-mentioned manufacturers the number of material classes is lower (8 when using intelligent packages such as EPX, X-ACT — up to 16), but the image contrast is higher.

The use of X-ray registration in two energy ranges using computer image processing also allows identifying potential threat objects (explosives, cold and firearms, drugs) in the controlled object. This has greatly simplified the work of X-ray machine operators and improved the quality of control. However, the result largely depends on the operator's qualifications (identification of threat objects does not allow for the automated detection of explosives with sufficient reliability). Such means successfully identify firearms and cold arms, grenades in metal cases, cartridges and unmasked explosives in significant quantities. However, as practice has shown, even the most experienced operator is unable to detect plastic explosives.

Further development of X-ray equipment was associated with the introduction of elements of tomographic acquisition and analysis of images of controlled objects. Improvement of E-Scan technology led to the creation of an automatic installation called Z-Scan, also developed by EG&G Astrophysics Research Corp. Like the latter, this installation analyzes the contents of luggage, recording the transmitted radiation in two energy regions (more precisely, one set of detectors records the entire spectrum of the transmitted radiation, and the other — only its high-energy part, cut out by the filter). Computer processing of the measurement results according to a specific algorithm makes it possible to highlight items made of organic and inorganic materials in the luggage image. But this is not yet enough to reliably detect well-camouflaged explosives. The image obtained by the E-Scan installation is a two-dimensional projection of a three-dimensional density distribution. At the same time, items made of less dense materials with low atomic numbers are shielded by items made of denser materials with high z, that is, there is an obvious information deficit.

To overcome this drawback, the Z-Scan system uses two X-ray sources that scan the baggage at two different angles, thus registering two projections of the object. After appropriate processing, an image of the contents of the controlled object in two projections and a three-dimensional distribution of only organic materials are displayed on monitor screens. Further development of this type of system follows the path of using fiber optic technologies, which will reduce the time for image analysis and thereby increase productivity, as well as somewhat increase the reliability of detection. This approach allows for more reliable automatic detection of explosives. This further simplifies the operator's task when searching for explosives.

The first installation of this type available to the user was the Vivid Technologies Inc. VIS-1 (Vivid Rapid Explosives Detection System), which uses a technology called Hologic to obtain a three-dimensional image of the contents of baggage. The latter is used in medical X-ray diagnostics and produces a close-to-monographic image of the objects in the checked object and, apparently, is similar to that adopted by the Z-Scan. Just like in the latest Z-Scan models, the VIS-1 software allows for the automatic detection of baggage containing suspicious objects (i.e., containing organic materials of the appropriate density). Large-scale tests of the VIS-1 installation at Glasgow Airport in the summer of 1993 and experience with its use at Zurich Airport from 1992 to 1993 showed that its integration into existing baggage handling lines allows for a significant increase in the speed of inspection and a reduction in personnel costs while improving flight safety. The baggage handling speed can reach 1200 units per hour per line, and the false alarm rate does not exceed 20%.

The method of recording backscattered X-rays is the basis of the explosives detection system developed by American Science and Engineering Inc. The system also differentiates between organic and inorganic materials in baggage using the difference in backscattering cross-sections caused by the comptom effect for materials with low and high atomic numbers. Items made of low-Z materials are displayed on a black-and-white display as continuous white on a black background. The image corresponding to the standard X-ray examination of baggage is recorded on the second monitor. Thus, the operator sees two monitors simultaneously and, by analyzing the images on them, makes a final decision.

Automatic identification of baggage suspected of containing explosives is provided. Coloring the baggage image in red warns the operator of the probability of explosives. Systems using this detection principle can be integrated into baggage transportation systems and are capable of providing a throughput of up to 1,000 pieces of baggage per hour.

However, these explosive detection devices have received a low rating from the FAA. Based on the testing results, their priority is considered average. Nevertheless, American Science and Engineering Inc. has managed to develop a special device for personal monitoring based on the backscattered radiation registration method. This device, despite the fact that a person receives a much lower dose of radiation during monitoring than during a standard fluorographic examination, cannot be used for mass monitoring. However, in some cases, its use can be justified by safety issues.

All the considered explosive detection systems have an important advantage — they are relatively inexpensive: their cost does not exceed $250,000 — $450,000. But as tests conducted under a special FAA program have shown, none of them can automatically detect the entire spectrum of explosives with a probability exceeding 4080%, which is considered unacceptable from a safety standpoint. Due to this circumstance, further improvement of X-ray systems went along the path of creating a computer tomography system. The first commercial installation of this type — the STX-5000 — was developed by Invision, USA.

The essence of the computed tomography method is reduced to scanning the inspected baggage with a narrow fan beam of X-ray radiation and detecting the transmitted radiation using a ruler (or semicircle) of a large number of discrete detectors. As a result of mathematical processing of a large number of measured projections, a complete three-dimensional density distribution is obtained. This is impossible in any other method of visualizing the contents of a controlled object using X-ray radiation. Tests of the installation demonstrated the possibility of detecting small quantities of explosives with an insignificant number of false alarms. Items that may be explosives are displayed on the monitor screen in red. The image quality is so high that both timers and detonators can be easily detected.

Based on the results of FAA testing, the СТХ-5000 SP model is currently recognized as the only automatic explosive detector and is recommended for use in US airports. According to the testing results, at a speed of inspection of 254 objects per hour, it detected various explosives with a probability of 92-95% with a false alarm rate of 18%.

Today, the company is working on creating a computer tomograph capable of detecting explosives in automatic mode with a throughput of up to 360 pieces of baggage per hour.

It should be noted, however, that recently, when used at US airports, it has come under serious criticism: — high cost ($ 0.9-1 million); — difficulty in operation; — impossibility of ensuring the above characteristics on real baggage flows (the probability of false alarms is approximately twice as high as established according to FAA information). In addition, it should be noted that the use of the model is effective only if the operator carries out control.

The latter led to the FAA's decision to conduct additional tests of this installation.

Despite the above difficulties, X-ray systems currently remain the only ones available to users of explosive detection equipment. It should also be noted that the attractiveness of these systems will always be associated with the fact that, in addition to explosives, they can detect other materials and items that are of interest to security services (blade and firearms, drugs and other materials and items prohibited from free movement across a controlled border).

Despite significant progress, none of the systems discussed above can provide fully automated detection of explosives.

Therefore, a new approach to solving the problem of ensuring aviation security was formulated.

To more fully ensure the safety of civil aviation flights from acts of terrorism, it is necessary to use a complex system of several successive barriers when checking baggage and hand luggage of air passengers for explosives.

1. The first barrier must be equipped with technical means that allow for a 99% probability of detecting hidden explosives within 6-10 seconds with an acceptable probability of false alarms of no more than 30%.

2. The second barrier must provide for monitoring only those objects that have caused suspicion of the presence of explosives at the first barrier. The duration of monitoring at the second barrier is allowed up to 20 seconds with a probability of false alarms of no more than 5% and a probability of correct detection of hidden explosives of at least 99%. At this stage, monitoring can be carried out with the participation of an operator.

In this case, the explosive search systems used at the second barrier can use information about the controlled objects obtained at the first barrier installations. If an operator is present at the second barrier, then there is no need for a third barrier.

3. The third barrier is envisaged only in the flight safety systems of large airports and should include installations capable of detecting the presence of explosives and their characteristics in no more than 1-2 minutes with an efficiency of at least 99% with a false alarm probability of no more than 1%. One of the most successful examples of an attempt to implement such a concept is the installation at the Manchester Airport (England) of a conveyor line with two Z-Scan installations on the first safety barrier and a STX 5000 installation on the second safety barrier.

I would like to say a few words about domestic developments in X-ray equipment. Currently, there are two manufacturers of this equipment: the Mosrentgen plant, which produces the Kontrol installations, and the Delta NPO, which produces the Nadzor installations. The technology they use corresponds to single-energy systems of Western manufacturers and does not allow to separate organic and inorganic substances, although work on the creation of domestic dual-energy systems is underway. In general, this equipment is technologically outdated, but the use of advanced element base, improvement of production and software can lead to the emergence of a competitive device.