Incoming inspection for explosion hazard.
Incoming inspection for explosion hazard
Vandyshev B.A.
Candidate of Technical Sciences
The article examines the main types of equipment required to equip inspection points for explosion hazard: X-ray introscopes (with X-ray radiation registration by optoelectronic detectors and with a fluorescent screen) and explosive vapor detectors
In order to prevent terrorist attacks with the use of explosive devices (ED), it is of great importance to check items entering the territory of the protected facility for explosive hazard. Currently, there are no universal means that can detect with 100% certainty ED hidden in hand luggage, household items, office equipment, electronic equipment, all kinds of containers, etc. At the same time, combining equipment, the operation of which is based on various physical principles, allows minimizing the disadvantages of individual devices. Since the range of such equipment is quite extensive, the article proposes to consider the main types of equipment that allow for fairly effective incoming inspection of various items for explosive hazard.
The most widely used at checkpoints are X-ray introscopes. Two of their varieties are used:
— with registration of X-ray radiation by optoelectronic detectors;
— with fluorescent screen.
The first type of devices scans the object being monitored with an X-ray beam. The transmitted radiation is recorded by detectors, the information from which is processed by an electronic device that forms a shadow picture of the internal structure of the object according to a given program. The resolution of modern equipment is quite high and allows detecting a copper wire with a diameter of 100 microns. The service and software support the operator's work with the image on the video monitor screen:
— changing its brightness and contrast;
— highlighting individual areas with an increase of 2.4 and 8 times;
— pseudo-coloring, etc.
This allows to decipher the X-ray shadow picture of the internal structure of the controlled object. The capabilities of X-ray introscopes have increased significantly due to the use of the so-called multi-energy method of transillumination, based on the processing of information from detectors, formulated from X-ray beams with different energy distributions of X-ray quanta in the spectrum (usually two energy distributions are used). In this case, the energy distribution is recorded, for example, by changing the anode voltage of the X-ray tube or filtering the radiation with a metal plate.
This operation establishes the difference in the interaction of X-ray quanta with materials that have different atomic numbers and numbers of atomic electrons. In this case, the images of various elements on the video monitor screen are assigned colors depending on the average atomic number of the substance that the objects in the test object are made of: elements with an atomic number less than 10 (this includes most explosives) — orange; with an atomic number from 10 to 18 — green; with an atomic number greater than 18 (most metal objects) — blue.
In some installations (for example, in the Z-Scan introscope from EG&G Astrophysics, USA), when viewing an image, the area suspected of containing explosives is highlighted with a red oval line, which provides the operator with an additional opportunity to identify explosives. The latest models of this installation use a fiber-optic X-ray detector, which significantly improves image quality and increases inspection productivity.
An additional opportunity for detecting UD is provided by recording X-ray quanta scattered from the test object, in particular particles reflected at an angle close to 180 degrees. Processing information from detectors recording backscattered radiation allows forming a picture of the internal structure of the surface layers of the test object. The principle of forming an image of the internal structure of the test object in backscattered X-ray radiation is implemented in X-ray introscopes from American Science and Engineering (USA).
X-ray introscopes with a fluorescent screen are simpler, more compact and significantly cheaper than scanning devices. The operator, using a mirror reflector, directly observes the shadow image of the internal structure of the controlled object on the fluorescent screen. This class of equipment is intended primarily for monitoring postal correspondence (letters, parcels, packages).
The most well-known introscopes on the market are those of Schiumberger Industries (France), EG&G Astrophysics (USA) and Toddresearch (England). A unique device of this type has also been created in Russia — a device for examining and rendering harmless explosive mail items U-OZ. The installation is equipped with manual manipulators with a set of replaceable tools and a ventilation system and removal of gaseous explosion products outside the premises. The operator is provided with full protection in the event of an accidental explosion of explosives weighing 300 grams in TNT equivalent.
Portable X-ray television equipment is used to check for explosive hazard of «accidentally forgotten» objects at the place of their discovery. It includes a small-sized X-ray machine, an X-ray conversion unit (fluorescent screen and video camera), an electronic information processing unit with a display or video monitor, and connecting cables. Installations such as u-Ray 150 (Germany), foXray and A-500E (Israel), «Schilling-95» (Russia) allow you to manipulate the image on the video monitor screen (enlarge, contrast, etc.).
The control post equipment must include a detector of explosive vapors (EV). The market for this type of equipment is represented by both stationary and portable devices, the operating principle of which is based on the methods of gas chromatography and ion drift spectrometry.
Chromatographic detectors of explosive vapors require the use of high-purity carrier gases (argon, nitrogen), which creates certain inconveniences during the operation of these devices. This problem is solved in an original way in the Egis explosive detector from Ther-medics (USA): the carrier gas hydrogen is obtained in the device itself by electrochemical decomposition of water.
In drift spectrometric detectors, the carrier gas is mainly air.
An important technological link in the process of detecting explosives is sampling. In portable drift spectrometers, the sampler is part of the complex, in stationary ones it is usually autonomous. The sampler is, in essence, a small vacuum cleaner that traps vapors and particles of explosives on sorbent surfaces or in a filter (concentrator). A paper filter can also be used to take smears from the surface of the controlled object. Then, during the heating process, the explosives are desorbed from the concentrator and the vapor fraction is analyzed.
It is quite a difficult task to detect low-volatile explosives that are part of plastic explosives, but the latest generation of devices can successfully cope with it. Nevertheless, in order to increase the efficiency of detecting hidden plastic explosives, in 1991 the International Convention on their marking with organic highly volatile substances was adopted, which, being present in the zone of concealed explosives in the vapor and condensed phases, are easily detectable. It should be noted that in combination with a gas analyzer, it is advisable to use a relatively inexpensive chemical kit for express analysis of trace amounts of explosives, with the help of which the components of plastic explosives are detected quite reliably (the description is given in the journal «Security Systems», No. 1, 1996, p. 61).
Thus, the minimum set of equipment for incoming inspection of items for explosive hazard should consist of an X-ray introscope (preferably a dual-energy scanning one), a detector of vapors or particles of explosives, and a chemical kit for detecting trace amounts of explosives. Depending on the operating conditions of the control post and the financial capabilities of the user, this set can be expanded by using office and portable X-ray equipment, portable detectors of explosive vapors, and supplemented with equipment based on other physical principles.
In particular, nuclear quadrupole resonance equipment such as Q Scan-1000 and QED from the American company Quantum Magnetics has recently appeared on the market, allowing detection of components of plastic explosives hidden in packaging in the absence of electromagnetic shielding.
A similar installation has been developed in Russia, but is not yet produced in commercial form.