RU2226686C1 - Method and device for detection and identification of concealed explosives and narcotics - Google Patents

Abstract

FIELD: measuring equipment. SUBSTANCE: the method includes irradiation of the substance under test containing nitrogen and/or carbon by a bundle of ionizing radiation, and registration of the secondary radiation from the decay products. Irradiation is conducted by a bundle of ionizing radiation with an energy not exceeding 60 NcV, the time spectrum of the secondary radiation signals is registered, according to the results of the analysis of the time spectrum, the relative contents of nitrogen and carbon are determined, and, according to the information on the carbon and nitrogen composition, the substance under test is identified. The device has a source of ionizing radiation, detector of the decay products and an analyzer of the detector signals. The analyzer represents a time identifier of relative concentrations of nitrogen and carbon, which has a time-to-digital converter. EFFECT: enhanced precision and reliability. 2 cl, 1 dwg, 3 tbl

Description

The invention relates to the field of detection of hidden explosives (BB) and narcotic drugs (NS) and can be used in mobile and stationary installations when clearing territories as part of humanitarian actions and to control the illegal traffic of explosives and NS at airports, customs terminals, checkpoints , car parks, postal services, etc.

The well-known method of photonuclear detection of hidden explosives and NSs is one of the most effective and high-speed methods for direct detection of explosives and NSs and consists in recording the decay products of short-lived isotopes ¹² V (boron-12) and ¹² N (nitrogen-12), which are produced as a result of photonuclear reactions on nitrogen ( ¹⁴ N) and carbon ( ¹³ C) (an admixture of the ¹³ C isotope in natural carbon is 1.107%) - chemical elements that form the basis of all modern explosives and are part of the most common NS.

When irradiating ¹⁴ N and ¹³ C nuclei with gamma rays with energies of a higher threshold value Eγ, the following photonuclear reactions occur:

The choice of these processes as reference provides a high selectivity for the detection of explosives, because upon irradiation of any other chemical elements with a gamma beam with an energy of less than 100 MeV, no other isotopes are formed with a half-life in the range of 1-200 ms. The ¹² V and ¹² N isotopes are β-active and in the process of decay emit electrons and positrons with a maximum energy of ~ 13 MeV and ~ 17 MeV, which, when moving in matter, in turn induce gamma rays. These gamma rays, as well as annihilation quanta with an energy of 511 keV, together with electrons and positrons constitute secondary decay products and can be detected by a detector. Therefore, if the object under investigation is irradiated with a gamma-ray pulse with gamma-ray energy above the threshold Eγ for reactions 1-3. then in the subsequent time interval of less than 200 ms, it will respond, if there is a sufficient concentration of nitrogen and / or carbon in it, by the flow of secondary particles from the decay of the isotopes ¹² V and ¹² N. Otherwise, this flow will not be in the measured time interval.

The practical implementation of the photonuclear method for detecting explosives and NS is associated with the suppression of possible so-called “false” responses from foreign substances also containing nitrogen and / or carbon. This can be organic substances, such as wood, when conducting work to detect explosives on the ground. Of particular importance is the suppression of false alarms in installations for controlling luggage, where the sources of false alarms can be various objects, which include nitrogen and carbon. The problem of false positives is one of the most important in all methods of detecting explosives and NS and its solution determines the efficiency and productivity of work and practical significance.

(2) путем регистрации аннигиляционных гамма-квантов с энергией 511 КэВ линейками из двух детекторов, расположенных по противоположным сторонам обследуемой единицы багажа. Как известно, аннигиляционные гамма-кванты вылетают в противоположные стороны (под углом 180°) при остановке распадного позитрона в веществе и тем самым указывают на расположение объекта с повышенным содержанием азота в объеме багажа. Но этот способ и установка не позволяют идентифицировать сам объект на принадлежность к ВВ. Отбраковка багажных единиц из общего потока на наличие азота может приводить в реальных условиях к резкому снижению производительности из-за ложных сигналов от предметов, содержащих азот.In US patent (No. 4756866 from 07/12/1988) [1] a device and method for detecting explosives for controlling baggage of air passengers according to reaction data only are proposed

(2) by registering annihilation gamma rays with an energy of 511 keV with arrays of two detectors located on opposite sides of the luggage unit being examined. As is known, gamma annihilation quanta fly out in opposite directions (at an angle of 180 °) when the decay positron in a substance stops, and thus indicate the location of an object with a high nitrogen content in the luggage volume. But this method and installation do not allow identifying the object itself as belonging to the explosive. The rejection of luggage units from the general stream for nitrogen can lead in real conditions to a sharp decrease in productivity due to false signals from objects containing nitrogen.

In the article [2], selected as a prototype, it was proposed to use all three reactions (1-3) and a method for identifying signals from explosives and NS from signals caused by other substances also containing nitrogen and / or carbon to search for explosives and NS. In this method, to identify the explosives and NS substances, it is proposed to conduct separate measurements of the outputs — the total number of signals from nitrogen and carbon at the maximum gamma-ray energy is higher than the threshold value for reaction (2) and the number of signals from carbon only at the maximum beam energy is less than the threshold reaction value (1). In the first measurement, the total number of ¹² V and ¹² N nuclei formed is determined, and in the second measurement, the number of ¹² V nuclei from reaction (3). The ratio of the number of these nuclei characterizes the substance. This method has certain disadvantages. It is necessary to dynamically change the energy of accelerated electrons and to control the intensity of the gamma-ray beam during the separate measurement of the outputs. In addition, for the correct separate measurement of the relative concentration of nitrogen and carbon from reactions (1-3) and reaction (3), it is necessary to take into account the shape of the inhibitory spectrum, which is difficult due to distortions due to the passage of radiation through the thickness of the hiding substance, which, in the general case is an unknown quantity. This is significant, for example, when detecting mines in the soil, when the depth of their installation from the surface can vary from 0 to 40-50 cm. These factors affect the accuracy of the results and the uniqueness of identification of explosives and NS.

The problem solved by the invention is to increase the accuracy and reliability while reducing the time of search and detection of explosives and NS.

The problem is solved by the claimed method, the essence of which is as follows. Upon a single irradiation of the test substance containing nitrogen and / or carbon with a gamma ray beam with an energy of more than 31 MeV, nuclei of short-lived isotopes ¹² V and ¹² N are formed in it as a result of reactions (1-3). The relative concentration of these isotopes is uniquely associated with the relative concentration of nitrogen and carbon in the irradiated substance and determines a unique portrait of the investigated substance. When decaying, the ¹² V and ¹² N isotopes form a secondary radiation flux, the shape of the time dependence of which is determined by the half-lives of the isotopes and their initial relative concentration. In general terms, the law of change in the number of radioactive nuclei of one element over time is represented by the exponent [3]:

where N (t) is the number of non-decayed nuclei at time t; N ₀ is the initial number of nuclei formed, λ is the decay constant. In our case, the decay of two elements:

where N _{0 [B-12)} and N _{0 [N-12]} are the number of nuclei formed, respectively, ¹² V and ¹² N,

N _{0 [sum]} is the total number of formed nuclei of radioactive isotopes ¹² V and ¹² N.

The main parameters of the decay of isotopes from reactions (1-3):

where T _1/2 is the half-life, λ ₁₁ , λ ₂₀ are the decay constants.

By analyzing after the end of the irradiation pulse the shape and behavior of the time dependence of the secondary radiation flux on the decays of ¹² V and ¹² N, it is possible to determine the initial relative concentration of isotopes ¹² V and ¹² N and to identify the test substance.

Quantitatively, the results of the analysis of the time spectrum of the decay products of isotopes ¹² V and ¹² N can be presented in the form of values of the parameter k, defined as

To implement the method, it is necessary that the background processes leading to photo formation of short-lived isotopes with a half-life of less than 200 ms and significantly distort the measured time spectrum are suppressed. Such processes include reactions on oxygen - 16 ( ¹⁶ O):

Of these processes, only reaction (11) can make a significant contribution to the useful signal due to the presence of ¹⁶ O nuclei in the molecule of the substance under study, while the contribution from process (10) is practically absent due to the extremely small cross sections for this reaction. In addition, reaction (11) can make a significant background contribution in the search for mines in the soil, since the elemental chemical composition of the soil can be 50% oxygen. It is possible to exclude from the registration the decay products from reaction (11) if the energy of the particles of ionizing radiation is limited to no more than 60 MeV, while the contribution from this reaction is practically absent. This energy limitation allows an unambiguous analysis of the contributions from the decay of only two isotopes ¹² V and ¹² N. Moreover, the background from the decay of other long-lived isotopes is insignificant and its contribution can be taken into account by the usual background subtraction procedure, which allows reliable identification of small amounts of explosives and NS.

Thus, the inventive method allows after a single exposure of the test substance to an ionizing radiation beam by measuring and processing the time dependence of the radioactive decay, to obtain information about the carbon and nitrogen composition and to identify the substance by the criterion of its belonging to explosives or NS.

A device [4] is known that uses a photonuclear detection method for explosives and allows for the identification of explosives to determine the relative concentration of nitrogen and carbon in the test substance (prototype). The device comprises an ionizing radiation source, a secondary radiation detector, and a detector signal analyzer located on a movable platform. To identify explosives in the setup, a method of double irradiation of the test substance with different values of the maximum gamma-ray energy in the probe beam can be used.

The task of implementing the proposed method for the detection and identification of explosives and NS is solved by the proposed device. The device contains a pulsed source of ionizing radiation, a table detector of decay products and a time identifier. The presence of a stop detector and a temporary identifier in the device is an essential distinguishing feature, since it allows identification of explosives and NS after a single irradiation of the test substance.

Using the inventive device allows 1) to detect all types of mines, explosive objects and drugs containing nitrogen and / or carbon, regardless of the design of mines and packaging of explosives and NS; 2) to detect and identify explosives with a mass of at least 10 g and NS - at least 50 g; 3) detect explosives and NS with a probability of at least 99.6%; 4) ensure the number of false positives at a level of less than 5%; 5) to create, on the basis of this device, highly efficient mobile and stationary installations for detecting explosives and NS. The inventive device is presented in the diagram. The following notation is used in the diagram and in the text:

1 - source of ionizing radiation,

2 - table detector of secondary radiation,

3 - object with explosives or NS,

4 - start generator

5 - temporary identifier,

6 - time-to-digital Converter

7 - installation counter,

8 - processor

9 - database

10 - detector detector BB or NS.

The proposed device for the photonuclear detection of explosives and NS contains a source of ionizing radiation 1 for generating pulses of a beam of gamma radiation and electrons; a table detector of secondary particles 2 for detecting decay products formed by radioactive isotopes and generating stop signals for subsequent temporary analysis; irradiation object 3, which may contain explosives and / or NS; a start generator 4 for generating a start signal "start" and the initialization of one act of irradiation of the object; time identifier 5 for temporary analysis of signals from the stop detector 2 and control of the start generator 4 and the signaling device 10 and integrating a time-digital converter 6 into a single functional unit, the installation counter 7; a processor 8 for processing the time distribution accumulated by the time-digital converter 6, calculating the value of k, comparing it with the data in the database 9, and turning on the signaling device 10 in the presence of explosives and / or NS; a database 9, which contains reference values of k _no for each of the substances to be identified and which is formed from experimental data in independent experiments or calculated values; detector for detecting explosives and / or HC 10 to inform about registered explosives and / or drugs.

The start generator 4 is connected to the ionizing radiation source 1 and the time-digital converter 6. The radiation source 1 irradiates the object 3. The secondary radiation of the object 3 is detected by the stop detector 2 connected to the time-digital converter 6. The time-digital converter 6 is connected to the installation counter 7, which is connected to the start generator 4 and the processor 8. The processor 8 is connected to the database 9. To the processor 8 is connected an alarm detector for detecting explosives and / or HC 10.

The proposed device operates as follows. Generator 4 generates a start pulse, which starts the ionizing radiation source 1 and the time-digital converter 6. The ionizing radiation source 1 forms a beam of gamma rays and electrons with a maximum energy of less than 60 MeV in the direction of the object being examined. If object 3 contains a substance containing nitrogen and / or carbon, then photonuclear reactions occur in it (1-3). The decay products of the formed unstable isotopes ¹² N and ¹² V (β particles and induced γ-quanta) are detected by the stop detector 2. The pulses of the stop detector 2 are sent to the time identifier 5 to the stop input of the time-digital converter 6 and the installation counter 7.

The installation counter 7 accumulates the signals coming from the stop detector 2 in a predetermined time interval. If the number of accumulated signals does not exceed the set threshold value, then the counter gives a signal to the start generator 4 for the next act of irradiating the object, and measurements and analysis of the time spectrum are not performed. Thus, the maximum speed of examination of object 3 is ensured. If the number of accumulated signals exceeds the set value, this will mean the presence in the irradiated object 3 of a substance containing carbon and / or nitrogen. In this case, 7 allows you to complete the accumulation of the time spectrum by a digital clock converter 6.

Time-to-digital Converter 6 conducts on the channel "stop" the accumulation of the number of incoming pulses in the corresponding discrete time channels into which the measured time interval is divided. The total number of signals in all discrete channels of device 6 corresponds to the total number of events (N _{0 [sum]} ). At the end of the accumulation process, the data is transmitted for processing to the processor 8. The processor 8 performs the processing of the time spectrum and calculates k.

The obtained value of k is compared with the same values (k _source ) in database 9. If the value of k coincides within the error with k _source from database 9, then the processor generates a detection signal to the signaling device 10. Maintaining 9 in the updated state is possible with new data received as a result of the operation of the device.

The invention is illustrated by the following examples.

Example 1

To confirm the effectiveness of the proposed method, a computer simulation of the processes related to the detection and identification of explosives and NS in conditions simulating baggage inspection in control installations at airports, customs terminals, etc. was carried out.

At the first stage, photoproduction of ¹² V and ¹² N isotopes in the irradiated substance was simulated, the total number of formed nuclei N _{0 [sum]} and the true value of k _{source were} calculated. At the second stage, the procedure for measuring the time dependence of the secondary radiation flux on the decays of the ¹² V and ¹² N isotopes was simulated and the value of k _ISM was restored from the measurement results. The simulation results shown in Table 1 were obtained under the following conditions: electron beam energy of 55 MeV, electron beam current in a pulse of 50 mA, current pulse duration of 6 μs, the area of the stop detector of secondary radiation 1 m ² , the distance from the object of study to the detector is 60 cm, the mass of explosives, NS and false objects 100 g, hiding substance - a layer of water 10 cm thick. The results are presented in table 1.

Column 3 presents the total number of registered signals N _{0 [sum]} obtained as a result of computer simulation of the detection process of this substance under the conditions described above.

Column 4 shows the relative contribution of ¹² N decay signals recorded as a result of computer simulation and which are uniquely related to the concentration of nitrogen and carbon in the substance. The relative contribution from the decay of ¹² N obtained as a result of the simulation is taken as the reference value k _source .

Column 5 presents the measured values of k _ISM (k _ISM = k (9)), recovered from the time spectrum of the recorded signals, and the measurement errors are indicated.

As follows from the obtained results, the inventive method allows you to effectively identify explosives and NS, separating them from false objects.

Example 2

Table 2 presents the main characteristics of a stationary installation for monitoring luggage units at airports, which can be developed on the basis of the invention. The data presented are based on the results of computer simulation of the detection and identification of explosives and NS.

From the table it follows that the installation may have unique characteristics that significantly exceed the most efficient and most common installations in the world in basic parameters. Thus, the CTX 9000 Dsi installation of InVision Technologies (USA) [5], designed to control explosives in baggage units at airports, operates on the basis of indirect detection (x-ray scanning and image processing) and has a capacity of 542 pieces of baggage per hour, and the data false positives are not given at all.

Example 3

Table 3 presents the comparative technical and economic characteristics for the methods for detecting explosives used in the cleaning of mined areas while observing the UN requirements for humanitarian demining [6].

Column 1 indicates the technical and economic indicators.

Column 2 shows the data for the main currently used manual method for detecting mines using modern portable devices and special search dogs.

Column 3 shows the calculated data for the device proposed in [4].

Column 4 shows the calculated data for a mobile installation using the inventive method and device for the detection and identification of hidden explosives.

From the data presented in the table it follows that the claimed method and device will allow for mine clearance work more than 800 times more effective than the main - manual method - and 2.8 times more effective than the device proposed in [4]. In addition, it should be noted that the claimed method and device, as well as the device according to the patent [4], allows for the implementation of uninhabited humanitarian demining technology, while the manual method, due to direct contact with explosive objects, exposes people to danger of death or injury.

Sources of information:

1. US patent No. 4756866, 376/157, CL. G 21 G 1/12, publ. 07/12/1988.

2. E.A. Knapp, A.W. Saunders, andW.P. Trower. Direct Imaging of Explosives. Proceedings Euroconference on: Sensor systems and signal processing techniques applied to the detection of mines and unexplosed ordnance. MINE'99, October 1-3,1999. Villa Agape, Firenze, Italy Laboratorio Ultrasuoni e Controlli Non Distmttivi Universita di Firenze, Italy. http://demming.jrc.it/aris/events/mine99/start.htm

3. K.N. Mukhin. Experimental nuclear physics. T.1. Physics of the atomic nucleus. Textbook for high schools. Ed. 3rd - M .: Atomizdat, 1974, p. 170.

4. Device for detecting hidden explosives. RF patent No. 2185614. BI No. 20, 2002

5. Official InVision Technologies SWITCH, http://www.invision-tech.com/index3.htm

6. International standards for conducting demining operations in the framework of humanitarian actions under the auspices of the UN. UN, 1996, 75 pp.

Claims (2)

1. A method for detecting and identifying hidden explosives and narcotic drugs, including irradiating a test substance containing nitrogen and / or carbon, ionizing radiation beams, recording secondary radiation from decay products formed by nitrogen-12 and boron-12 isotopes, characterized in that irradiation is carried out by a beam of ionizing radiation with an energy of not more than 60 MeV, the time spectrum of the secondary radiation signals is recorded, the relative nitrogen contents are determined by the results of the analysis of the time spectrum and carbon, and information on the carbon and nitrogen composition when using a database with reference values identify the test substance. 2. A device for detecting and identifying hidden explosives and narcotic drugs, including an ionizing radiation source, a decay product detector and a detector signal analyzer, characterized in that the analyzer is a temporary identifier for relative concentrations of nitrogen and carbon, which contains a time-digital converter connected to the installation a counter and a processor interacting with the database, while the installation counter is connected to the source through the start generator Associated with vremyatsifrovym converter, and is connected to the processor switch.

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