RU2262097C1 - Meethod for detection of explosive in inspected subject - Google Patents

Abstract

FIELD: detection of explosive in inspected subject.

SUBSTANCE: a camera provided with a radiation protection is irradiated by thermal neutrons, and at least by one detector of gamma-radiation, gamma-radiation is regustered by transformation of gamma quantums into electric pulses and comparison of their amplitudes with the threshold values, energy spectrum of gamma-radiation is determined at least within the interval of the energy of gamma-quantume, including the upper limit of the values of the energy of gamma-quantums emitted at interaction with thermal neutrons atom nucleus at least of one chemical element in composition of the materials of the chamber, radiation protection or detector of gamma radiation, the point of the maximum and the point of the decrease of the energy spectrum in the mentioned intervals of energy are determined, the amplitudes of the electric pulses are determined from gamma-quantums with energies corresponding to the energies of the points of maximum a decrease, corresponding to the energies of the points of maximum and decrease, ratings. Then the subject under inspection is placed in the chamber, the subject under inspection is irradiated by thermal neutrons, the gamma-radiation is registered, the lower and upper threshold values are determined, and a decision is taken on presence of explosive in the subject under inspection at an excess of the threshold value.

EFFECT: reduced probabilities of omission of explosive and false alarm.

8 dwg

Description

FIELD OF THE INVENTION

The present invention relates to the field of neutron radiation analysis of materials and can mainly be used to combat terrorism and organized crime to detect nitrogen-containing explosives in controlled objects without opening them.

State of the art

Combating the illicit trafficking of explosives and terrorist acts with their use has become one of the main tasks of the security services in the fight against international terrorism and organized crime. One of the areas of this opposition is connected with the organization at airports, in state and diplomatic institutions, at nuclear power plants of control of such items as briefcases, bags, trunks, suitcases, electronic equipment, computers, mobile phones and the like, as well as mail, since it is they who are most often used by criminals to place explosives during their illegal transportation or committing terrorist acts. The need to control large flows of postal items or to inspect passengers' hand luggage and baggage, especially in air transport, in the conditions of a limited time allocated for control or inspection, requires the use of methods and implementing their technical means that do not include opening and visual inspection of each controlled subject, but providing rapid detection of explosives with a high probability of correct detection with a small number of false alarms.

Among the many known methods for detecting explosives in controlled objects, three groups of methods have now found practical application.

The first group combines the methods (Patrick Flanagan, "Technology vs. terror", EUSA, 1989, N7, pp. 46-49, 51, brochures and information sheets of EG&G Astrophisics Research Corporation, Long Beach, California, USA and In Vision Technologies, Foster City, California, USA), which use X-ray radiation to detect explosives and involve irradiating a controlled object with X-ray energy of 100-150 keV, registering the X-ray radiation transmitted through the controlled object and identifying the explosive based on derogation from the X-ray materials, contained in the test subject, depending on the atomic numbers of their constituent chemical elements.

Since modern explosives, especially plastic ones, consist mainly of chemical elements with a small atomic number, they weakly absorb x-rays with an energy of 100-150 keV. This circumstance complicates the effective detection of explosives in cases of unconventional forms of execution or disguise by placing, for example, in pieces of soap or electronic equipment. The practice of using detection methods using x-ray radiation showed that with their help explosives can be detected in no more than 40-60% of cases.

The second group of methods is based on the fact that most explosives belong to the class of highly volatile organic compounds characterized by high vapor pressure. These methods (Hughes D. Thermedics Begins Production Of Bomb Detection Unit. - Aviation Week & Space Technology, June 19, 1989) involve gas chromatography or mobility spectrometry methods for the chemical analysis of ions of an explosive substance and its particles emitted by a controlled object that in microscopic amounts can be on the surface of the controlled object. Based on the results of this analysis, a decision is made about the presence of an explosive in a controlled object. A similar method is implemented, for example, in the IONSCAN 350 explosive and drug detection system manufactured by Barringer Instruments Ltd, Canada (Intersec. The Journal of International Security, Vol.3, No.6, November 1993).

The technical means that implement these methods have high sensitivity, but do not allow the plastic explosives with the highest power to be detected due to their very low vapor pressure. In addition, these methods do not ensure the detection of all types of explosives if they are placed in sealed packaging or in packaging that has undergone special processing.

The third group of methods for detecting explosives is based on determining the presence of the main chemical elements that make up its composition using neutron radiation analysis.

Related to this group are known methods of detecting explosives and implementing their installation (US 5078952, 1992, US 5114662, 1992, US 5144140, 1992, US 5153439, 1992, EP 0295429, 1992, EP 0297249, 1993, EP 0336634, 1993, US 5388128, 1995, RU 2206080, 2003) provide for the placement of a controlled object in a chamber with radiation protection, irradiation with thermal neutrons, registration of gamma radiation emitted by a controlled object with a quantum energy of about 10.8 MeV, obtaining, based on the results of registration of gamma radiation, a concentration distribution nitrogen in a controlled manner You can also determine the presence of explosive in it upon the fact of an increased concentration of nitrogen.

As you know, all modern explosives contain a fairly large amount of nitrogen, comprising from 9 to 35 mass percent with a density of explosives from 1.25 to 2.00 g / cm ³ . When an explosive is irradiated with thermal neutrons with an energy of about 0.025 eV, radiation captures thermal neutrons by the nuclei of nitrogen-14 atoms, resulting in the formation of nuclei of nitrogen-15 atoms in an excited state. Upon transition from the excited state to the ground state, on average, about 14% of the nuclei of nitrogen-15 atoms emit gamma rays with an energy of about 10.8 MeV. Registration and counting of gamma rays with an energy of about 10.8 MeV allows you to obtain information about the concentration of nitrogen in a controlled subject and decide on the presence of an explosive in it upon the fact of an increased concentration of nitrogen.

There are also known methods for detecting explosives and their installations based on neutron radiation analysis of materials (US 5080856, 1992, US 5200626, 1993), which provide for placing a controlled object in a chamber with radiation protection, simultaneous irradiation of the controlled object with thermal neutrons with energy of about 0.025 eV and fast neutrons with an energy of about 14 MeV, registration of gamma radiation with a quantum energy of about 10.8 MeV, emitted during radiation capture of thermal neutrons by nuclei of nitrogen atoms-14, and g mma radiation with a quantum energy of about 6.1 MeV, emitted by the nuclei of oxygen-16 atoms in an excited state, formed as a result of the interaction of fast neutrons with stable nuclei of oxygen atoms, obtaining information on the concentration of nitrogen and oxygen in a controlled environment based on the results of gamma radiation registration subject and making a decision on the presence of an explosive in it upon the fact of an increased concentration of nitrogen and oxygen, as well as the magnitude of their ratio.

It is known that all explosives have not only a high density of nitrogen, but also a high density of oxygen, the value of which for the main types of explosives lies in the range from about 0.80 to 1.15 g / cm ³ . Moreover, almost all known materials that are not explosives, but which cause false alarms due to the relatively high density of nitrogen contained in them, such as nylon, silk, wool, leather, melamine and others, have a low oxygen density. Thus, it became possible, using nuclear interactions of fast neutrons with an energy of about 14 MeV with nuclei of oxygen-16 atoms, to register the gamma radiation emitted by them with gamma-quanta energy of about 6.1 MeV and to obtain additional information about the oxygen density in a controlled subject. A joint examination of the results of recording the intensity of gamma radiation from nitrogen and oxygen makes it possible to decide on the presence or absence of an explosive in a controlled object. Such additional registration of gamma radiation with a quantum energy of about 6.1 MeV increases the likelihood of correct detection of explosives in the implementation of these methods.

However, the use of fast neutrons for irradiation of a controlled object, which have a significantly higher energy than thermal neutrons, requires the use of additional radiation protection for the camera in order to ensure that the existing requirements for the protection of personnel and the public from exposure to ionizing radiation, which leads to an increase in the mass, size and cost of this device method. In addition, the use of fast neutrons causes an increase in the radiation dose absorbed by a controlled object, which can lead to a deterioration in the consumer properties of industrial products contained in it, such as electronic equipment and photographic materials.

When carrying out all of the known methods for detecting explosives based on neutron radiation analysis, the detection of gamma radiation is performed by at least one gamma radiation detector containing a thallium activated sodium iodide scintillator and in optical contact with it photoelectronic multiplier. When registering gamma-rays emitted by a controlled object and falling into the scintillator of a gamma-ray detector cause light flashes in it, the brightness of which is proportional to the energies of gamma-quanta. The gamma-ray photoelectronic multiplier converts the optical radiation of light flashes emitted by the scintillator into electric pulses with an amplitude proportional to the energies of the gamma rays incident on the scintillator, which, after amplification by the amplifier, go to an amplitude analyzer that extracts electric pulses with an amplitude proportional to the energy of the nitrogen atom emitted by the nucleus a gamma ray of about 10.8 MeV or the energy of the oxygen atom emitted by the nucleus of a gamma ray of about 6.1 MeV, based comparing them with upper and lower threshold values. Counting the number of emitted pulses from gamma rays with an energy of about 10.8 MeV or with energies of about 10.8 MeV and 6.1 MeV gives information about the concentration, respectively, only of nitrogen or nitrogen and oxygen in the controlled subject.

However, the transmission coefficient of the optoelectronic path for detecting gamma radiation emitted by a controlled object from a scintillator to an amplitude analyzer substantially depends on the instability of parameters and aging of the elements of the optoelectronic path, instability of its supply voltage, and also on environmental conditions such as level ionizing radiation, temperature, pressure and humidity of the surrounding air. In addition, the scintillator transmission coefficient also largely depends on the frequency of arrival of gamma rays falling into it, which can vary significantly depending on the presence of various chemical elements in the materials contained in the controlled object.

Firstly, this leads to instability of the amplitude value of electric pulses from gamma rays with energies of about 10.8 MeV and 6.1 MeV emitted by the nuclei of nitrogen and oxygen atoms, respectively, and its deviation from the calculated value. As a result of this, when registering gamma radiation, if the amplitude value of these electric pulses goes beyond the range between the lower and upper threshold values, they will not be detected by an amplitude analyzer and therefore will not be recorded. This circumstance causes an increase in the probability of missing an explosive when it is detected.

Secondly, under conditions when a controlled object contains materials consisting, in addition to nitrogen and oxygen, of a number of other chemical elements, the nuclei of atoms of these chemical elements when interacting with thermal neutrons or with thermal and fast neutrons also emit gamma radiation with gamma-ray energies of a sufficiently wide range of the spectrum, including those with energies quite close in value to 10.8 MeV and 6.1 MeV. In particular, the atomic nuclei of such chemical elements as, for example, chromium, selenium, iron and silicon, emit gamma rays with energies close enough to 10.8 MeV, and the atomic nuclei of such chemical elements as, for example, chlorine , manganese, sodium and iron, emit gamma rays with energies close to 6.1 MeV. When registering gamma radiation due to the instability of the amplitude value of electric pulses from gamma rays emitted by the atomic nuclei of such chemical elements, it is possible that the amplitude value of these electric pulses falls into the range between the lower and upper threshold values. As a result of this, they will be isolated by an amplitude analyzer and mistakenly detected as electrical pulses from gamma rays with energies of 10.8 MeV and 6.1 MeV, supposedly emitted by the nuclei of nitrogen and oxygen atoms, respectively. This circumstance causes an increase in the probability of false alarm when explosives are detected.

The closest in technical essence to the present invention should be considered a method for detecting weapons and explosives in controlled objects (RU 2065156, 1996, G 01 N 23/222, G 01 N 23/223), based on the joint use of methods of radiography and neutron radiation material analysis. This known method for detecting weapons and explosives in controlled objects, after the initial detection of weapons and explosives using x-ray, placing the controlled object in a chamber with radiation protection and at least one gamma radiation detector, irradiating the controlled object with thermal neutrons, registration gamma radiation emitted by a controlled object by converting gamma rays by at least one gamma radiation detector in an ele ctric pulses with amplitudes proportional to the energies of gamma quanta, and comparing the amplitudes of electrical pulses with threshold values, the selection of electrical pulses with an amplitude proportional to the energy of the gamma quantum of about 10.8 MeV, determining the intensity of gamma radiation with an energy of gamma quanta of about 10, 8 MeV and deciding on the presence of an explosive in a controlled object when the intensity of gamma radiation with gamma-ray energy exceeds about 10.8 MeV of its threshold value.

As with the implementation of all the known methods of detecting explosives described above, based on the use of neutron radiation analysis, when implementing this known method for detecting explosives, the gamma radiation emitted by a controlled object is recorded by at least one gamma radiation detector , which contains a thallium activated scintillator based on sodium iodide and a photomultiplier tube in optical contact with it. When registering, the gamma rays emitted by the controlled object and entering the scintillator of the gamma radiation detector cause light flashes in it, the brightness of which is proportional to the energies of gamma rays. The gamma-ray photoelectron multiplier converts the optical radiation of light flashes emitted by the scintillator into electric pulses with an amplitude proportional to the energies of the gamma quanta that are incident on the scintillator, which, after amplification by the amplifier, are fed to an amplitude analyzer that extracts electric pulses with an amplitude proportional to the gamma-ray energy near 10.8 MeV, based on a comparison of them with upper and lower threshold values. Counting the number of emitted pulses from gamma rays with an energy of about 10.8 MeV gives information about the concentration of nitrogen in the controlled subject.

At the same time, the transmission coefficient of the optoelectronic path for detecting gamma radiation emitted by the controlled object from the scintillator to the amplitude analyzer and the background electrical signal at its output substantially depend on the instability of the parameters and aging of the elements of the optoelectronic path, the instability of its supply voltage, and also from environmental conditions such as the level of ionizing radiation, temperature, pressure and humidity of the surrounding air. In this case, the transmission coefficient of the scintillator of the gamma radiation detector, as well as its background light flashes, also largely depend on the frequency of arrival of gamma rays falling into it, which can vary significantly depending on the presence of various chemical elements in the materials contained in the controlled object. So, for example, the presence of 200-500 g of chlorine or cadmium in a controlled object leads to an increase in the frequency of gamma rays entering the scintillator by 1.3-1.5 times, which causes an increase in its transmission coefficient by 10-17%, and the presence of water in an amount of 1 kg reduces the frequency of arrival of gamma rays in the scintillator 1.1-1.2 times, reducing its transmission coefficient by 6-12%.

On the one hand, this leads to instability of the amplitude value of electric pulses from gamma rays with an energy of about 10.8 MeV emitted by the nuclei of nitrogen atoms, and its deviation from the calculated value, as a result of which, when the amplitude value of the electric pulses exceeds the limits of the range between the lower and upper threshold values, they will not be highlighted by the amplitude analyzer and therefore will not be recorded. This circumstance causes an increase in the probability of missing an explosive when it is detected.

On the other hand, under conditions when a controlled object contains materials consisting, in addition to nitrogen, of a number of other chemical elements, the nuclei of atoms of these chemical elements, when interacting with thermal neutrons, also emit gamma radiation with gamma-ray energies of a fairly wide spectrum range . In this case, the atomic nuclei of such chemical elements as, for example, chromium, selenium, iron and silicon, emit gamma rays with energies that are quite close in value to 10.8 MeV. When registering gamma radiation due to the instability of the amplitude value of electric pulses from gamma rays emitted by the atomic nuclei of such chemical elements, it is possible that the amplitude value of these electric pulses falls into the range between the lower and upper threshold values, as a result of which they will be highlighted by an amplitude analyzer and erroneously detected as electrical pulses from gamma rays with an energy of about 10.8 MeV, supposedly emitted by the nuclei of nitrogen atoms. This circumstance causes an increase in the probability of false alarm when explosives are detected.

The disadvantages of the method for detecting weapons and explosives in controlled objects selected for the closest analogue are the high probabilities of missing an explosive and false alarm when detecting explosives using neutron radiation analysis.

Disclosure of invention

The objective of the present invention is to reduce the likelihood of missed explosives and false alarms when detecting explosives using neutron radiation analysis.

The problem is solved according to the invention in that the proposed method for detecting explosives in a controlled object, including, in accordance with the closest analogue, placing the controlled object in a chamber equipped with radiation protection and at least one gamma radiation detector, irradiating the controlled object with thermal neutrons, registration of emitted gamma radiation by converting gamma rays by at least one gamma radiation detector into electrical pulses with amplitude by pulses proportional to the energies of gamma-quanta, and comparing the amplitudes of electrical pulses with threshold values, the selection of electrical pulses with an amplitude proportional to the energy of gamma-quanta, which is in a predetermined range of energy values, including a value of 10.8 MeV, by comparing their amplitudes with the lower and the upper threshold values, the calculation of the allocated electrical impulses, the decision on the presence of explosives in the controlled subject in excess of the number of calculated electrical impulses of its threshold value, differs from the closest analogue in that before placing the controlled object, the camera is irradiated with thermal neutrons, the energy spectrum of the detected gamma radiation is determined, at least in the gamma-ray energy interval including the value of 2.23 MeV, and in the interval energy of gamma rays, including the upper limit of the energy values of gamma rays emitted in the interaction with thermal neutrons by the nuclei of atoms of at least one chemical element that is part of the material in the camera, radiation protection or gamma radiation detector, determine the maximum point of the energy spectrum due to gamma quanta with an energy of about 2.23 MeV, and the decay point of the energy spectrum in the range of gamma-ray energy, including the upper limit of gamma-ray energy values, the atomic nuclei of a specified chemical element emitted during interaction with thermal neutrons determine the amplitudes of electric pulses from gamma rays with energies corresponding to the energies of the maximum and decay points of the spectrum of the detected gamma radiation, ensure that the amplitudes of the electric pulses from the gamma rays correspond to the energies corresponding to the energies of the maximum and decay points of the energy spectrum, to the calculated values, when the controlled object is irradiated with thermal neutrons, the energy spectrum of the detected gamma radiation is determined, at least the energy interval of gamma rays, including the value of 2.23 MeV, determine the maximum point of the energy spectrum due to gamma rays with energies emission of about 2.23 MeV, determine the amplitude of the electrical pulses from gamma rays with energy corresponding to the energy of the maximum point of the energy spectrum due to gamma rays with an energy of about 2.23 MeV, and taking into account the specified amplitude, determine the lower and upper threshold values for electrical pulses with an amplitude proportional to the energy of gamma rays, which is in a predetermined range of energy values, including a value of 10.8 MeV, while determining the lower and upper threshold values for the allocation of ctric pulses with an amplitude proportional to the energy of gamma quanta, which is in a predetermined range of energy values, including a value of 10.8 MeV, is carried out in accordance with the expression U _then = E _then U _in / E _in , where U _then - respectively the lower or upper threshold a value for separating electrical pulses with an amplitude proportional to the energy of gamma rays, which is in a predetermined range of energy values, including a value of 10.8 MeV; E _pore - respectively, the lower or upper threshold energy value for the allocation of gamma rays with energy in a predetermined range of energy values, including a value of 10.8 MeV; U _in - the amplitude of the electrical pulses from gamma rays with energy corresponding to the energy of the maximum point of the energy spectrum due to gamma rays with an energy of about 2.23 MeV; Е _в - energy of a gamma-ray emitted by the nucleus of a hydrogen atom in interaction with a thermal neutron, Е _в = 2.23 MeV.

In this case, the energy spectrum of the detected gamma radiation is determined in the gamma-ray energy range, including an upper limit of 6.826 MeV, of the gamma-ray energy emitted during the interaction with thermal neutrons by the nuclei of iodine atoms, which is part of the scintillator material of the gamma-ray detector, or in the gamma-ray energy interval, including an upper limit equal to 4.945 MeV, of the gamma-ray energy emitted during the interaction with thermal neutrons by the nuclei of carbon atoms included in av of the radiation protection material of the chamber, or in the gamma-ray energy range, including an upper limit of 8.578 MeV, of the gamma-ray energy emitted when interacting with thermal neutrons by the nuclei of chlorine atoms included in the radiation protection material of the chamber, or in the energy range of gamma quanta, including an upper limit of 7.724 MeV, of gamma quanta energy emitted during interaction with thermal neutrons by the nuclei of aluminum atoms, which is part of the structural material of the camera and the detector and gamma radiation, and determine the point of slowdown energy spectrum in said range of gamma-ray energy. The recession points of the energy spectrum in the gamma-ray energy range, including the upper limit of the gamma-ray energy values emitted when interacting with thermal neutrons by atomic nuclei of chemical elements that are part of the materials of the camera, radiation protection or gamma-ray detector, are determined by numerically differentiating the energy spectrum, compliance with the calculated values of the amplitudes of the electrical pulses from gamma rays with energies corresponding to the energies of the maximum and decay points Skog spectrum provided by changing the electronic transmission path coefficient converting gamma rays into electric pulses and electric pulses to the addition of the gamma quanta bias voltage.

Thermal neutron irradiation before placing a controlled object in an empty chamber equipped with radiation protection and at least one gamma radiation detector, and registering the gamma radiation emitted by it by converting gamma rays by at least one gamma radiation detector into electrical pulses with amplitudes proportional to the energies of gamma-quanta, it is possible to determine the energy spectrum of the detected gamma radiation, at least in the range of gamma-ray energy, including 2.23 MeV, and in the range of gamma-ray energy, including the upper limit of the gamma-ray energy emitted by the interaction of thermal neutrons with atomic nuclei of at least one chemical element that is part of the materials of the camera, radiation protection or detector gamma radiation.

Boron polyethylene is used in large quantities as a material for the radiation protection of the chamber, since it effectively absorbs neutrons. Due to the fact that the composition of polyethylene includes hydrogen, as well as such chemical elements as carbon and chlorine, as a result of interaction with thermal neutrons, the nuclei of atoms of these chemical elements emit gamma radiation, which makes a very significant contribution to the energy spectrum of gamma radiation from an empty chamber.

It was found that the nuclei of hydrogen atoms intensively emit gamma radiation with energies of gamma rays of about 2.23 MeV, which leads to the appearance in the energy spectrum of gamma radiation of a pronounced maximum in the energy range of gamma rays, including the value of 2.23 MeV, near the specified value of the energy of gamma rays.

When interacting with thermal neutrons, the nuclei of chlorine atoms emit gamma radiation with gamma-ray energies not exceeding the upper limit of 8.578 MeV. Due to the presence of chlorine in the radiation protection material, the atomic nuclei of which do not emit gamma rays with energies of more than 8.578 MeV, the energy spectrum of gamma radiation has a decrease in intensity for gamma rays with energies of 8.578 MeV or more. The nuclei of carbon atoms in interaction with thermal neutrons also emit gamma radiation with gamma-ray energies not exceeding the upper limit of 4.945 MeV. Due to the high concentration of carbon in the radiation protection material, the atomic nuclei of which do not emit gamma rays with energies of more than 4.945 MeV, the energy spectrum of gamma radiation has a decrease in intensity for gamma rays with energies of 4.945 MeV or more.

As noted, gamma radiation detectors containing a sodium iodide scintillator are used to record gamma radiation. It turned out that the nuclei of iodine atoms contained in the scintillator material of the gamma radiation detector, when interacting with thermal neutrons, emit gamma radiation with gamma-ray energies not exceeding the upper limit of 6.826 MeV. Due to the fact that the source of gamma quanta with energies of the indicated values is the scintillator material itself, which transforms gamma quanta into light flashes during registration, almost all gamma quanta emitted by the atomic nuclei of the iodine scintillator are detected by a gamma radiation detector. Since the nuclei of iodine atoms do not emit gamma rays with energies of more than 6.826 MeV, the energy spectrum of gamma radiation from an empty chamber has a fairly noticeable decrease in intensity for gamma rays with energies of 6.826 MeV and more.

Aluminum-based alloys are widely used as a structural material for radiation protection chambers, which has a relatively low cost and, when irradiated with thermal neutrons, does not emit gamma radiation with gamma-ray energies close in value to the energies of gamma-ray nitrogen atoms emitted. In addition, the housing of the gamma radiation detector is made of aluminum, since due to the low atomic number of aluminum, such a housing effectively transmits gamma radiation to the gamma radiation detector. The nuclei of aluminum atoms in the interaction with thermal neutrons emit gamma radiation with gamma-ray energies not exceeding the upper limit value of 7.724 MeV. Therefore, in the energy spectrum of gamma radiation of an empty chamber, a decrease in its intensity is observed for gamma rays with energies of 7.724 MeV or more.

Performing, for example, a numerical differentiation of the energy spectrum of gamma radiation by energy allows us to identify at least one point of decline in the energy spectrum in the energy range of gamma rays, including the upper limit of the energy of gamma rays emitted in the interaction with thermal neutrons by the nuclei of chemical atoms elements that make up the materials of the camera, radiation protection or gamma radiation detector. The indicated decay point of the energy spectrum of gamma radiation either corresponds to gamma-ray energy of 6.826 MeV and is caused by gamma radiation emitted during the interaction with thermal neutrons by the nuclei of atoms of the iodine scintillator material, or corresponds to gamma-ray energy of 4.945 MeV and is caused by gamma radiation emitted during the interaction with thermal neutrons by the atomic nuclei of the carbon radiation protection component of the material, or corresponds to the energy of gamma rays of 8.578 MeV and is due to gamma zlucheniem emitted in the interaction of thermal neutrons with nuclei of atoms which is part of the radiation shielding material chlorine or corresponds to the energy of gamma rays and 7.724 MeV due to the gamma radiation emitted in the interaction of thermal neutrons with nuclei of atoms which is part of a structural aluminum material chamber.

An analysis of the energy spectrum of gamma radiation makes it possible to identify the maximum point of the energy spectrum of gamma radiation, which corresponds to an energy of about 2.23 MeV of gamma rays emitted during the interaction with thermal neutrons by the nuclei of hydrogen atoms, which is part of the radiation protection material.

Determination of the amplitude of electric pulses from gamma rays with energies corresponding to known and strictly specified energies of the points of one maximum and at least one decay of the energy spectrum of the detected gamma radiation emitted by the radiation protection camera and gamma radiation detector makes it possible to ensure compliance amplitudes of electrical pulses from gamma rays with energies corresponding to the energies of the maximum and decay points of the energy spectrum, calculated values, for example, m changes the transmission coefficient of the electronic path for converting gamma rays into electrical pulses and adding bias voltage to the electrical pulses from gamma rays. Such a change in the transmission coefficient of the electronic path for converting gamma quanta into electrical pulses makes it possible to compensate for the instability of its transmission coefficient, and the addition of a constant bias voltage to the electric pulse from the gamma quantum provides compensation for the instability of the background electrical signal. In this case, the transmission coefficient of the electronic path for converting gamma rays into electrical pulses is changed, and a constant bias voltage is added until the amplitudes of the electrical pulses from gamma rays with energies corresponding to the energies of the maximum and decay points of the energy spectrum become equal to the specified calculated values . This provides compensation immediately before the neutron-radiation analysis of the controlled object in the optoelectronic path for detecting gamma radiation, both distortions such as zero bias caused by the instability of the background electrical signal and distortions of the transmission coefficient of the optoelectronic path due to its instability.

On the one hand, this compensates for the change due to the instability of the amplitude value of electric pulses from gamma rays with an energy of about 10.8 MeV emitted by the nuclei of nitrogen atoms, and brings it closer to the calculated value. As a result of this, during registration, the amplitude value of electric pulses from gamma rays with an energy of about 10.8 MeV will not go beyond the range between the lower and upper threshold values, so they will be extracted by an amplitude analyzer and recorded. This circumstance leads to a decrease in the probability of missing an explosive when it is detected.

As noted, under conditions when a controlled object contains materials consisting, in addition to nitrogen, of a number of other chemical elements, the nuclei of atoms of these chemical elements, when interacting with thermal neutrons, also emit gamma radiation with gamma-ray energies of a fairly wide range of the spectrum. In this case, the atomic nuclei of such chemical elements as, for example, chromium, selenium, iron and silicon, emit gamma rays with energies that are quite close in value to 10.8 MeV. Therefore, on the other hand, when registering gamma radiation due to a decrease in the instability of the amplitude value of electric pulses from the chemical elements of gamma quanta emitted by the atomic nuclei, this is achieved by compensation caused by the instability of the background electrical signal of distortion such as zero offset and instability of the transmission coefficient of the optoelectronic path, hit the amplitude value of these electrical pulses in the range between the lower and upper threshold values will not occur . As a result of this, such electrical pulses will not be isolated by an amplitude analyzer and will not be erroneously recorded as electrical pulses from gamma rays with an energy of about 10.8 MeV. This circumstance leads to a decrease in the probability of false alarm when explosives are detected.

When a controlled object is irradiated with thermal neutrons, the registration of gamma radiation emitted by the controlled object and a camera with radiation protection makes it possible to determine the energy spectrum of the detected gamma radiation, at least in the gamma-ray energy range including 2.23 MeV.

An analysis of the energy spectrum of gamma radiation allows us to determine the maximum point of the energy spectrum in the energy range of gamma rays, including the value of 2.23 MeV, which is due to gamma rays emitted as a result of interaction with thermal neutrons by the nuclei of hydrogen atoms. The determination of the amplitude of electric pulses from gamma rays with energy corresponding to the energy of the maximum point of the energy spectrum makes it possible to determine the lower and upper threshold values for the extraction of electric pulses with an amplitude proportional to the energy of gamma rays, which is in a given range of energy values, including a value of 10, 8 MeV. Such a determination of the lower and upper threshold values for the extraction of electrical pulses is carried out, for example, in accordance with the expression U _pore = E _pores U _in / E _c , where U _pores are respectively the lower or upper threshold value for the selection of electrical pulses with an amplitude proportional to gamma energy - quanta located in a predetermined range of energy values, including a value of 10.8 MeV; E _pore - respectively, the lower or upper threshold energy value for the allocation of gamma rays with energy in a predetermined range of energy values, including a value of 10.8 MeV; U _in - the amplitude of the electrical pulses from gamma rays with energy corresponding to the energy of the maximum point of the energy spectrum due to gamma rays with an energy of about 2.23 MeV; Е _в - energy of a gamma-ray emitted by the nucleus of a hydrogen atom in interaction with a thermal neutron, Е _в = 2.23 MeV.

This makes it possible, directly upon detection of an explosive in a specific controlled object with its specific content of chemical elements in the materials contained therein, before comparing the amplitudes of the electrical pulses from gamma rays with their threshold values, to determine the specified lower and upper threshold values for the separation of electrical pulses with an amplitude proportional to the energy of gamma rays, which is in a predetermined range of energy values, including a value of 10.8 MeV, i.e. to isolate electrical pulses from gamma rays with an energy of 10.8 MeV emitted by the nuclei of nitrogen atoms.

The use in determining the refined lower and upper thresholds for the isolation of electrical pulses determination result of the amplitude U _{in the} electrical impulse from the gamma-ray with energy _E = 2.23 MeV, which corresponds to the maximum power point of the energy spectrum of gamma rays resulting from the nuclei of hydrogen atoms, allows directly during the neutron-radiation analysis of a specific controlled object with its only characteristic content of chemical elements in it materials to compensate for the influence of distortions such as zero shift caused by the instability of the background electrical signal in the optoelectronic path of detecting gamma radiation. Moreover, in this case, the influence of the background electrical signal is compensated for taking into account the specific content of the chemical elements contained in the controlled item materials that are specific to the specific controlled item that is currently undergoing neutron radiation analysis.

First, the use of such refined lower and upper threshold values when registering gamma rays compensates for the effect of the change due to distortions in the amplitude value of electric pulses from 10.8 MeV gamma rays emitted by the nuclei of nitrogen atoms. As a result of this, during registration, the amplitude value of electric pulses from gamma quanta with an energy of 10.8 MeV, despite distortions, will not go beyond the range between the lower and upper threshold values. Therefore, such electrical pulses will be detected by an amplitude analyzer and recorded. This circumstance leads to a decrease in the probability of missing an explosive when it is detected.

Second, the use of such refined lower and upper threshold values when registering gamma quanta compensates for the effect of changes due to distortions in the amplitude value of electric pulses from gamma quanta with energies close to 10.8 MeV that emit non-nitrogen atomic nuclei and other chemical elements, such as chromium, selenium, iron and silicon, which can cause a false alarm. When registering, the amplitude value of the electrical impulses from gamma rays emitted by the atomic nuclei of such chemical elements, despite the distortions, will not fall between the specified lower and upper threshold values. Therefore, such electrical pulses will not be isolated by an amplitude analyzer and are erroneously recorded as electrical pulses from gamma rays with an energy of 10.8 MeV. These reasons lead to a decrease in the probability of false alarm when explosives are detected.

These circumstances confirm the achievement of the technical result declared in the task of the present invention due to the presence of the listed distinguishing features in the proposed method for detecting explosives in a controlled subject.

The essence of the proposed method for detecting explosives in a controlled subject is as follows:

- before placing the controlled object is irradiated with thermal neutrons with an energy of about 0.025 eV, a camera equipped with radiation protection and at least one gamma radiation detector;

- register gamma radiation emitted by the camera, radiation protection and a gamma radiation detector, by converting gamma rays by at least one gamma radiation detector into electrical pulses with amplitudes proportional to the energies of gamma quanta, and comparing the amplitudes of the electrical pulses with threshold values. In practice, the most preferred registration of gamma radiation with gamma-ray energy in the range of 1-13 MeV;

- determine the energy spectrum of the detected gamma radiation, at least in the energy range of gamma rays, including the value of 2.23 MeV, and in the energy range of gamma rays, including the upper limit of the energy values of gamma rays emitted during interaction with thermal neutrons atomic nuclei of at least one chemical element that is part of the materials of the camera, radiation protection or gamma radiation detector. In practice, it is preferable to determine the energy spectrum in the range of energy values from 1 to 13 MeV;

- identify in the resulting energy spectrum, for example, by comparing the maximum point. In this case, the maximum point of the energy spectrum of gamma radiation due to gamma rays with an energy of about 2.23 MeV, emitted during the interaction with thermal neutrons by the nuclei of hydrogen atoms, is revealed;

- identify, for example, using numerical differentiation of the obtained energy spectrum, the decay point of the energy spectrum of gamma radiation emitted by the camera, radiation protection and gamma radiation detector, which is caused by gamma radiation emitted as a result of interaction with thermal neutrons by atomic nuclei, at least , one chemical element that is part of the materials of the camera, radiation protection and gamma radiation detector. At the same time, at least one point of recession of the energy spectrum of gamma radiation due to either gamma rays with energies up to 6.826 MeV, emitted during interaction with thermal neutrons by the nuclei of iodine atoms, which is part of the scintillator material of the gamma radiation detector, or gamma is detected -quantums with energies up to 4.945 MeV, emitted when interacting with thermal neutrons by the nuclei of carbon atoms included in the radiation protection material, or gamma-quanta with energies up to 8.578 MeV, emitted during the interaction with thermal neutrons by nuclei of atoms of chlorine, which is part of the radiation shielding material, or gamma photons with energies up to 7.724 MeV emitted during the interaction of thermal neutrons with nuclei of aluminum atoms constituting the structural material chamber. Since the sources of gamma rays with energies up to 6.826 MeV are the nuclei of iodine atoms, which are part of the scintillator material of the gamma radiation detector, which converts gamma quanta into light flashes when registering, almost all of these gamma quanta are detected by the gamma radiation detector. Therefore, the recession point of the energy spectrum of gamma radiation, which is caused by gamma quanta with energies up to 6.826 MeV, emitted by the nuclei of iodine atoms interacting with thermal neutrons, is most pronounced and its identification in the energy spectrum of gamma radiation is most preferable;

- determine the amplitudes of the electrical pulses from gamma rays with energies corresponding to the energies of the maximum and decay points of the energy spectrum of the detected gamma radiation emitted by the camera, radiation protection and a gamma radiation detector;

- ensure that the amplitudes of the electrical pulses from gamma rays correspond to the energies corresponding to the energies of the maximum and decay points of the energy spectrum, to the calculated values, for example, by changing the transmission coefficient of the electronic path for converting gamma rays into electrical impulses and adding voltage to the electrical impulses from gamma rays displacement. In this case, the transmission coefficient of the electronic path for converting gamma rays into electrical pulses is changed, and a constant bias voltage is added until the amplitudes of the electrical pulses from gamma rays with energies corresponding to the energies of the maximum and decay points of the energy spectrum become equal to the specified calculated values ;

- then place the controlled object in a chamber equipped with radiation protection and at least one gamma radiation detector;

- irradiated with thermal neutrons with an energy of about 0.025 eV, a controlled object located in a chamber with radiation protection and at least one gamma radiation detector;

- register the gamma radiation emitted by the controlled object and the camera with radiation protection by converting gamma rays by at least one gamma radiation detector into electrical pulses with amplitudes proportional to the energies of gamma quanta and comparing the amplitudes of the electrical pulses with threshold values. In practice, the most preferred registration of gamma radiation with gamma-ray energy in the range of 1-13 MeV;

- determine the energy spectrum of the detected gamma radiation, at least in the energy range of gamma rays, including a value of 2.23 MeV. In practice, it is preferable to determine the energy spectrum in the range of energy values from 1 to 13 MeV;

- identify in the resulting energy spectrum, for example, by comparing the maximum point. In this case, the maximum point of the energy spectrum of gamma radiation due to gamma rays with an energy of about 2.23 MeV, emitted during the interaction with thermal neutrons by the nuclei of hydrogen atoms, is revealed;

- determine the amplitude of the electrical pulses from gamma rays with energy corresponding to the energy of the maximum point of the energy spectrum of gamma radiation due to gamma rays with an energy of about 2.23 MeV emitted by the interaction of thermal neutrons with the nuclei of hydrogen atoms;

- determine the lower and upper threshold values for the extraction of electrical pulses with an amplitude proportional to the energy of gamma rays, which is in a given range of energy values, including a value of 10.8 MeV, for example, in accordance with the expression U _pore = E _pore U _in / E _in where U _then - respectively, the lower or upper threshold voltage for separating electric pulses with an amplitude proportional to the energy of gamma rays, which is in a given range of energy values, including a value of 10.8 MeV; E _pore - respectively, the lower or upper threshold energy value for the allocation of gamma rays with energy in a predetermined range of energy values, including a value of 10.8 MeV; U _in - the amplitude of the electrical pulses from gamma rays with energy corresponding to the energy of the maximum point of the energy spectrum due to gamma rays with an energy of about 2.23 MeV; Е _в - energy of a gamma-ray emitted by the nucleus of a hydrogen atom in interaction with a thermal neutron, Е _в = 2.23 MeV;

- emit electrical pulses with an amplitude proportional to the energy of gamma rays, which is in a predetermined range of energy values, including a value of 10.8 MeV, by comparing their amplitudes with the obtained lower and upper threshold values;

- count the number of selected electrical pulses;

- decide on the presence of explosive in the controlled object when the number of calculated electrical pulses exceeds its threshold value, after which the controlled object is removed from the camera with radiation protection.

If a decision is made about the presence of an explosive in a controlled object, it is sent for autopsy and visual inspection.

Brief Description of the Drawings

The implementation of the proposed method for detecting explosives in a controlled object is illustrated by the following graphic materials.

Figure 1 shows the system implementing the proposed method for detecting explosives in a controlled subject, where 1 is a controlled subject, 2 is a neutron radiation analysis facility, 3 is a horizontal shaft, 4 is a conveyor, 5 is a computer and 6 is an alarm.

Figure 2 shows a longitudinal section along aa of the installation 2 for neutron radiation analysis (figure 1), where 7 is the casing, 8 is radiation protection, 9 is the camera, 10 is the thermal neutron emitter, 11 is the gamma radiation detector 12 is a lateral neutron reflector and 13 is a lower neutron reflector.

Figure 3 shows a longitudinal section of a detector 11 of gamma radiation, where 14 is the detector body, 15 is a neutron filter cup, 16 is a scintillator and 17 is a photoelectron multiplier.

Figure 4 shows the structural diagram included in the installation 2 for neutron radiation analysis of electronic equipment, where 11 is a gamma radiation detector, 18 is a pre-amplifier, 19 is a multiplier, 20 is an adder, 21 is an analog-to-digital converter, 22 is the first a digital to analog converter; and 23, a second digital to analog converter.

Figure 5 shows the energy spectrum of gamma radiation obtained experimentally in the gamma-ray energy range from 1 to 13 MeV, emitted by a camera with radiation protection and gamma radiation detectors, but without a controlled object and recorded for 1000 s, where the number of registered gamma quanta are given along the ordinate axis on a logarithmic scale.

Figure 6 shows the energy spectrum of gamma radiation numerically differentiated in the energy range from 4 to 12 MeV shown in Fig.5, emitted by a camera with radiation protection and a gamma radiation detector, but without a controlled object and recorded for 1000 s.

7 shows the experimentally obtained in the energy range of gamma rays from 1 to 13 MeV the energy spectrum of gamma radiation emitted by a controlled object without explosive and a camera with radiation protection and a gamma radiation detector and recorded for 1000 s, where the number of registered gamma quanta are given along the ordinate axis on a logarithmic scale.

On Fig shows the experimentally obtained in the energy range of gamma rays from 1 to 13 MeV the energy spectrum of gamma radiation emitted by a controlled object containing about 200 g of nitrogen-containing explosive, and a camera with radiation protection and a gamma radiation detector and recorded for 1000 c, where the number of registered gamma rays is given along the ordinate axis in a logarithmic scale.

The implementation of the invention

Implementing the proposed method, a system for detecting explosives in a controlled object contains (Fig. 1) a neutron radiation analysis apparatus 2, a conveyor 4, a computer 5 with an alarm signaling device 6 and electronic equipment, passing through a horizontal shaft 3 of a neutron radiation analysis apparatus 2 the structural diagram of which is shown in Fig.4. The conveyor 4 is designed to move the controlled object 1 through the horizontal shaft 3 of the installation 2 for neutron radiation analysis and is configured to stop with a small coast. As a computer 5 can be used a personal computer.

Installation 2 for neutron radiation analysis contains (figure 2) a housing 7, inside which is placed radiation protection 8 made of borated polyethylene to reduce the level of neutron radiation and lead to reduce the level of gamma radiation to acceptable values. A horizontal shaft 3 with a conveyor belt 4 located along the lower part of the shaft 3 passes through the housing 7 and radiation protection 8 and has a chamber 9 in the central part of the horizontal shaft 3, formed by two side reflectors 12 of neutrons and a lower reflector of 13 neutrons and designed to accommodate a controlled object 1 when irradiated with thermal neutrons. The side neutron reflectors 12 and the lower neutron reflector 13 are made of polyethylene in the form of plates with dimensions not less than the corresponding overall dimensions of the chamber 9 and installed along it vertically and horizontally flush with its respective walls. The side reflectors 12 neutrons and the lower reflector 13 neutrons are designed to increase the fraction of thermal neutrons by slowing down the fast neutron reflectors from the emitter 10 thermal neutrons in the material and to ensure uniform distribution of thermal neutrons over the volume of the irradiated area of the controlled object 1. Above the camera 9 in In the radiation protection of the 8th cavity, a thermal neutron emitter 10 is installed, which is made in the form of a fast neutron radionuclide source based on California-252 s the possibility of their subsequent deceleration by polyethylene to thermal energy values of about 0.025 eV and is similar in design to the thermal neutron emitter used in the implementation of the method chosen for the closest analogue. In the cavities made in the radiation protection 8, under the chamber 9 behind the lower neutron reflector 13, gamma radiation detectors 11 are installed. To ensure that the conveyor belt 4 can stop when the controlled object 1 enters the chamber 9 of the horizontal shaft 3, the neutron radiation analysis unit 2 is equipped with a stop sensor, which is located in the chamber 9, can be made in the form of end contacts or based on the source and receiver optical radiation and not shown in the figures.

The gamma radiation detector 11 (Fig. 3) comprises a detector housing made of aluminum with a photomultiplier tube 17 located inside it and in optical contact with a scintillator 16. The inorganic scintillator 16 is most preferably used as the scintillator 16, for example based on thallium activated sodium iodide. To reduce the impact on the scintillator 16 of thermal neutrons penetrating from the chamber 9, it is placed in a glass 15 of a neutron filter, which is sealed with double walls and a double bottom, the cavity between which is filled with material that reduces the flow of thermal neutrons, for example lithium carbonate, lithium fluoride or lithium phosphate.

The electronic equipment included in the apparatus 2 for neutron radiation analysis contains several channels that are identical in structure, the number of which is equal to the number of gamma radiation detectors 11 used. Each channel contains (Fig. 4) a gamma radiation detector 11 connected in series, a preamplifier 18, a multiplier 19, an adder 20 and an analog-to-digital converter 21, as well as the first and second digital-to-analog converters 22 and 23, the outputs of which are connected to the second inputs, respectively the adder 20 and the multiplier 19. The output of the analog-to-digital converter 21 of each channel is connected to the input of the computer 5, and the inputs of the first and second digital-to-analog converters 22 and 23 are connected to the outputs of the computer 5. In addition, the outputs of the computer 5 are connected to the input of an alarm signaling device 6 intended to form the signal presence or absence of an explosive in the controlled object 1, and with a drive belt 4 for supplying start signals and stop the conveyor 4.

A system that implements the proposed method for detecting explosives in a controlled object, works as follows.

Open the shutter (not shown in the figures) of a thermal neutron emitter 10 that emits thermal neutrons with an energy of about 0.025 eV into the internal cavity of chamber 9. When irradiated with thermal neutrons of chamber 9, radiation protection 8, gamma radiation detectors 11 and other elements of installation 2 for of neutron-radiation analysis, the radiative capture of thermal neutrons by atomic nuclei of chemical elements that make up the materials used in them occurs, as a result of which these atomic nuclei become excited. The transition of atomic nuclei from an excited state to the ground state is accompanied by the emission of gamma rays with different energy values.

In this case, gamma radiation is also emitted by the nuclei of hydrogen atoms, which are part of the radiation protection material 8 and emitting gamma rays with an energy of about 2.23 MeV, the nuclei of carbon atoms, which are part of the radiation protection material 8 and which emit gamma rays with energies up to 4.945 MeV, nuclei of chlorine atoms included in the composition of the radiation protection material 8 and emitting gamma rays with energies up to 8.578 MeV, nuclei of iodine atoms included in the scintillator material 16 of the gamma radiation detector 11 and emitting gamma rays with energy up to 6.826 MeV, and the nuclei of aluminum atoms, which are part of the structural materials of installation 2 for neutron radiation analysis, as well as the material of the casing 14 of the gamma radiation detector 11 and emitting gamma rays with energies up to 7.724 MeV.

A certain part of these gamma rays gets into the scintillators 16 of the gamma radiation detectors 11 (Fig. 3) and causes light flashes in them, the brightness of which is proportional to the energies of the gamma rays. The photoelectronic multiplier 17 of the gamma radiation detector 11 converts the optical radiation of the light flash from each gamma ray emitted by the scintillator 16 into an electric pulse with an amplitude proportional to the energy of the gamma ray incident on the scintillator 16. After amplification by the preamplifier 18 (Fig. 4), electric pulses from gamma quanta are supplied to the first input of the multiplier 19. Simultaneously, from the output of computer 5, the digital-to-analog converter 23 receives a digital code stored in the storage device of computer 5, which corresponds to the calculated value of the optical transmission coefficient -the electronic path of registering gamma radiation from the scintillator 16 to the adder 20 inclusive. This digital code is converted by the second digital-to-analog converter 23 into an analog electrical signal, which is fed to the second input of the multiplier 19, multiplying it with instantaneous voltage values of the electrical pulses from gamma rays. The output signal from the multiplier 19 is fed to the first input of the adder 20. At this time, from the output of the computer 5, the first digital-to-analog converter 22 receives a zero digital code corresponding to the zero background electric signal, and therefore, from the first digital-to-analog converter 22, the zero input of the adder 20 signal. As a result, electric pulses from gamma quanta are generated at the output of adder 20, the amplitude of which is directly proportional to the energy of gamma quanta with a proportionality coefficient equal to the transmission coefficient of the optoelectronic path for registering gamma radiation from the scintillator 16 to the adder 20 inclusive. In this case, the amplitude of each electric pulse from the gamma-quantum would be equal to its calculated value if the transmission coefficient of the optoelectronic gamma-radiation detection path were equal to its calculated value and the background electric signal was zero.

However, the transmission coefficient of the optoelectronic path for detecting gamma radiation from the scintillator 16 to the adder 20 and the background electrical signal at the output of the adder 20 substantially depend on the instability and spread of parameters and aging of the elements of the optoelectronic path, the instability of its supply voltage, and also on such environmental conditions, such as the level of ionizing radiation, temperature, pressure and humidity of the surrounding air. In this case, the transfer coefficient of the scintillator 16 of the gamma radiation detector 11, as well as its background light flashes, also largely depend on the frequency of arrival of gamma rays falling into it, which can vary significantly depending on the presence of various chemical elements in the composition of the controlled object 1 materials, as well as from the density of the flux of thermal neutrons entering the chamber 9.

An analog-to-digital converter 21 converts the amplitude value of each electric pulse from a gamma ray received from the output of the adder 20 into a digital code that is input into computer 5. Computer 5 by comparing with threshold values of the received digital codes corresponding to the amplitude values of electric pulses from gamma quanta and, consequently, the energies of the registered gamma quanta, determines which of the energy subbands with a width, for example, ΔЕ = 12-13 keV in the energy range from 1 to 13 MeV cheniyu its energy belongs to each registered gamma quantum, and counts and stores the number of registered during 5-10 minutes of gamma rays having an energy value within each subband. As a result of this, the energy spectrum of gamma radiation emitted in the absence of a controlled object 1 by the materials of the camera 9, radiation protection 8, detectors 11 of gamma radiation and other elements of the neutron radiation analysis apparatus 2, which is stored in the storage device of computer 5, is obtained.

An example of such an energy spectrum of gamma radiation experimentally obtained by the inventors during 1000 s is shown in FIG. 5, where the number of registered gamma quanta along the ordinate axis is shown on a logarithmic scale. The maximum gamma-ray energy spectrum of about 2.23 MeV is clearly visible in the gamma-ray energy spectrum shown, which is due to gamma-rays emitted by the nuclei of hydrogen atoms, which is part of the radiation protection material 8. On this energy spectrum, one can also see recession points energy spectrum, firstly, in the range of gamma-ray energy 4.945 MeV, which is associated with the emission of gamma-quanta by the nuclei of carbon atoms, which is part of the radiation protection material 8, and secondly, in the range of gamma-ray arrays of 6.826 MeV, which is associated with the emission of gamma-quanta by the nuclei of iodine atoms, which is part of the scintillator material of 16 gamma-ray detectors 11, thirdly, in the range of gamma-ray energy values of 7.724 MeV, which is associated with the emission of gamma-rays quanta by the nuclei of aluminum atoms, which is part of the structural materials of installation 2 for neutron radiation analysis, and, fourthly, in the range of gamma quanta energies of 8.578 MeV, which is associated with the emission of gamma quanta by the nuclei of chlorine atoms, which is part of the radiation material ionic protection 8.

Then, to identify the decay points of the energy spectrum of gamma radiation, computer 5 performs numerical differentiation of the received and stored energy spectrum of gamma radiation in the energy range from 1 to 13 MeV. In this case, the value of the derivative of the energy spectrum for each energy subband with number i is determined, for example, at an energy value corresponding to the right boundary of the energy subband, for example, according to the expression P = (N _{i + 1} - N _i ) / (2ΔE), i = 1, 2, ..., M, where N _{i + 1} is the number of registered gamma quanta with energy corresponding to the energy sub-band with number i + 1; N _i - the number of registered gamma rays with energy corresponding to the energy sub-band with number i; ΔЕ is the energy subband width; M is the number of energy subbands.

The result of numerical differentiation of the energy spectrum of gamma radiation, shown in Fig.5, shown in Fig.6. The differentiated energy spectrum of gamma radiation clearly shows the maxima corresponding to the points of decline of the energy spectrum, firstly, in the range of energy of gamma rays of 4.945 MeV, which is associated with the emission of gamma rays by the nuclei of carbon atoms, which is part of the radiation protection material 8 secondly, in the range of gamma-ray energy values of 6.826 MeV, which is associated with the emission of gamma-quanta by the nuclei of iodine atoms, which is part of the scintillator material of 16 gamma-ray detectors 11, and thirdly, the range of gamma-ray energy values of 7.724 MeV, which is associated with the emission of gamma-rays by the nuclei of aluminum atoms, which is part of the structural materials of installation 2 for neutron radiation analysis, and, fourthly, in the range of gamma-ray energy values of 8.578 MeV, which is associated with the emission of gamma quanta by the nuclei of chlorine atoms, which is part of the radiation protection material 8. As can be seen, the maximum of the differentiated energy spectrum in the range of gamma quanta energy of 6.826 MeV is most important, associated with uskaniem gamma quanta nuclei iodine atoms constituting the material 16, the scintillators of detectors 11 gamma radiation, which is the reason it is preferred detection point corresponding to this maximum decay energy spectrum in the present process.

Then, the computer 5 reveals by comparison the maximum energy spectrum (see Fig. 5) of gamma radiation in the energy range from 1 to 13 MeV and at least one of the maxima of the differentiated energy spectrum (see Fig. 6), preferably in the region the energy of gamma rays of 6.826 MeV, which is due to gamma rays emitted by the nuclei of iodine atoms. For example, when detecting the maximum of the energy spectrum of gamma radiation, computer 5 within the range of gamma-ray energy values from 1 to 13 MeV performs a sequential comparison of the number N _{i + 1 of} registered gamma-quanta with energy corresponding to the energy sub-band with number i + 1, and the number N of registered gamma rays with energy corresponding to the energy subband number i, for every two adjacent energy subbands of width ΔE out of the total number M of energy subbands. As a result of such a comparison, computer 5 determines an energy subband of width ΔE in which the largest number of gamma quanta is recorded, and assigns to the detected value of the energy of gamma quanta corresponding to the maximum of the energy spectrum of gamma radiation, an energy value equal to, for example, the middle of the indicated subrange. Similarly, computer 5 detects at least one of the maxima of the differentiated energy spectrum.

Next, the computer 5 determines the values previously received from the analog-to-digital Converter 21 corresponding to the amplitude values of the electrical pulses from the registered gamma rays and, therefore, their energies of digital codes, which correspond to the positions of the detected maximum energy spectrum (see Fig. 5) of gamma radiation in the energy region of gamma rays about 2.23 MeV and the maximum of the differentiated energy spectrum (see Fig.6), for example, in the energy region of gamma rays 6.826 MeV. The computer 5 compares the indicated digital codes with their reference calculated values stored in its storage device.

If, for example, as a result of such a comparison, it turned out that the digital code corresponding to the amplitude of the pulse from a gamma quantum with an energy of about 2.23 MeV is less than the reference calculated value, then this means that the background electric signal has become smaller than the calculated value due to distortions . In this case, the computer 5 generates a progressively positive digital code, which is converted by the first digital-to-analog converter 22 into a positive analog electrical signal supplied to the adder 20 and summed by it with incoming electrical pulses from gamma rays. Due to the addition of such a bias voltage, the amplitude value of electric pulses from all gamma rays, including those with an energy of about 2.23 MeV, becomes larger. After the analog-to-digital converter 21 converts the amplitude values of the electrical pulses from gamma quanta to digital codes, the latter also enter computer 5, in which digital codes corresponding to gamma quanta with an energy of about 2.23 MeV are compared with their reference calculated value. This bias voltage is added until the digital codes corresponding to gamma-quanta with an energy of about 2.23 MeV become equal to their reference calculated value, after which the digital code at the input of the first digital-to-analog converter 22 ceases to increase.

If, however, comparing the digital code corresponding to gamma quanta with an energy of about 2.23 MeV with its reference calculated value, it turned out that the digital code corresponding to the amplitude of the pulse from a gamma quantum with an energy of about 2.23 MeV is larger than the reference calculated value , this means that the background electrical signal due to distortion has become larger than the calculated value. In this case, everything happens the other way around.

Thus, compensation is made for changes in the background electrical signal due to its instability.

If after such compensation for changes in the background electric signal, when the digital code corresponding to gamma quanta with an energy of about 2.23 MeV is equal to its reference calculated value, as a result of the comparison, it turned out that, for example, a digital code corresponding to the amplitude of the pulse from the gamma quantum with an energy of 6.826 MeV, less than its reference calculated value, this means that the transmission coefficient of the optoelectronic path for registering gamma radiation from the scintillator 16 to the adder 20 inclusive due to instability lower than the calculated value. In this case, the computer 5 generates a digital code that grows in time from the value corresponding to the calculated value of the transfer coefficient. This digital code, after being converted by the second digital-to-analog converter 23 into an analog electrical signal, is supplied to the second input of the multiplier 19, which multiplies it with the instantaneous voltage value of the electrical pulses from gamma rays. Due to this, the transmission coefficient of the optoelectronic path for detecting gamma radiation increases and the amplitude value of electric pulses from all gamma rays, including those with an energy of 6.826 MeV, becomes larger. After the analog-to-digital converter 21 converts the amplitude values of the electrical pulses from gamma quanta to digital codes, the latter also enter computer 5, in which digital codes corresponding to 6.826 MeV gamma quanta are compared with their reference calculated value. Such an increase in the transmission coefficient of the optoelectronic path is carried out until the digital codes corresponding to gamma quanta with an energy of 6.826 MeV become equal to their reference calculated value, after which the digital code at the input of the second digital-to-analog converter 23 ceases to increase.

Thus, compensation is made for the instability of the transmission coefficient of the optoelectronic path for registering gamma radiation from the scintillator 16 to the adder 20 inclusive.

Such compensation for the instability of the transmission coefficient of the optoelectronic path for detecting gamma radiation and changes in the background electrical signal due to its instability is carried out until both digital codes corresponding to the amplitudes of the electrical pulses from gamma rays with energies of about 2.23 and 6.826 MeV will not be equal to their respective reference design values.

After that, the system is ready to perform neutron radiation analysis of the controlled object 1.

The controlled object 1 is installed on the conveyor belt 4 and the conveyor 4 is launched from the computer keyboard 5. When the controlled object 1 is delivered by the conveyor 4 to the chamber 9 of the installation 2 for neutron radiation analysis, the conveyor belt 4 will be stopped by a signal from a stop sensor not shown in the figures with a controlled item 1.

Thermal neutrons with an energy of about 0.025 eV are emitted by a thermal neutron emitter 10 into the internal cavity of chamber 9 and irradiated including a controlled object 1. When thermal neutrons are irradiated with a controlled object 1, chamber 9, radiation protection 8, gamma radiation detectors 11, and other installation elements 2, for neutron-radiation analysis, radiative capture of thermal neutrons by atomic nuclei of chemical elements that are part of the materials contained in them occurs, as a result of which these atomic nuclei become uzhdennoe state. The transition of atomic nuclei from an excited state to the ground state is accompanied by the emission of gamma rays with different energy values.

In particular, when thermal neutrons are irradiated with nitrogen-containing materials located in the controlled object 1, radiation capture of thermal neutrons by nuclei of nitrogen-14 atoms will occur, as a result of which nuclei of nitrogen-15 atoms are formed in an excited state. The transition from the excited state of the nuclei of nitrogen-15 atoms to the ground state will occur with the emission of gamma rays with an energy of about 10.8 MeV with a transition probability of about 0.14. In this case, gamma radiation is also emitted by, among other things, the nuclei of hydrogen atoms emitting gamma rays with an energy of about 2.23 MeV.

Some of these gamma quanta fall into the scintillators 16 of the gamma radiation detectors 11 (Fig. 3) and, similarly to those described above, are converted into digital codes supplied to computer 5 proportional to the energies of these gamma quanta.

Computer 5, by comparing with the threshold values of the received digital codes corresponding to the energies of the registered gamma-quanta, determines to which of the energy subbands with a width, for example, ΔЕ = 12-13 keV in the energy range from 1 to 13 MeV, each registered energy value gamma-quantum, and counts and remembers the number of gamma-quanta recorded over a period of 5-10 seconds that have an energy value within each subband. As a result of this, the energy spectrum of gamma radiation emitted by the controlled object 1 is obtained, as well as the materials of the camera 9, radiation protection 8, gamma radiation detectors 11 and other elements of the neutron radiation analysis apparatus 2, which is stored in the storage device of computer 5.

An example of such an energy spectrum of gamma radiation experimentally obtained by the authors during 1000 s, when the controlled object 1 does not contain a nitrogen-containing explosive, is shown in Fig. 7, where the number of registered gamma-quanta along the ordinate axis is shown on a logarithmic scale. An example of the energy spectrum of gamma radiation experimentally obtained by the authors during 1000 s, when the controlled object 1 contains a nitrogen-containing explosive, is shown in Fig. 8, where the number of registered gamma-quanta along the ordinate is shown on a logarithmic scale. The energy spectra presented here were obtained for 1000 s, that is, for a sufficiently long time interval, which is associated with the need for greater visibility of their graphical representation in these figures and for ease of perception. In practice, immediately upon detection of an explosive in a controlled object 1, a similar energy spectrum is removed in a significantly shorter time, equal to 5-10 s. In both energy spectra of gamma radiation in the cases of both the absence and the presence of explosive in the controlled object 1, one can clearly see the maxima in the energy region of gamma rays of about 2.23 MeV, which are due to gamma rays emitted by the nuclei of hydrogen atoms. Moreover, a relatively high number of registered gamma rays with an energy of about 10.8 MeV is observed in the second energy spectrum (Fig. 8), which is associated with the presence of 1 nitrogen-containing explosive in the controlled object.

Then, the computer 5 reveals by comparison, as discussed above, the maximum energy spectrum (see Figs. 7 and 8) of gamma radiation in the energy range from 1 to 13 MeV in the energy region of about 2.23 MeV, which is due to gamma radiation nuclei of hydrogen atoms. Next, the computer 5 determines the value of the digital codes previously received from the analog-to-digital converter 21, corresponding to the amplitude values of the electrical pulses from the registered gamma quanta and, therefore, their energies, which correspond to the position of the detected maximum energy spectrum (see Figs. 7 and 8) gamma -radiation in the gamma-ray energy region of about 2.23 MeV.

Then, the computer 5 performs the determination of the lower and upper threshold values for the extraction of electrical pulses with an amplitude proportional to the energy of gamma rays, which is in a predetermined range of energy values, including a value of 10.8 MeV. In practice, the indicated range of gamma-ray energy values is preferably set from 9.2 to 11.0 MeV. To do this, based on a digital code corresponding to the amplitude value of the electric pulse from a gamma quantum with an energy of about 2.23 MeV, computer 5 calculates the lower and upper threshold values for a digital code corresponding to the amplitude value of the generated electric pulses from gamma quanta with an energy of about 10.8 MeV, for example, in accordance with the expression U _pore = E _pore U _in / E _in , where U _pore is the lower or upper threshold value for the digital code corresponding to the amplitude value electric pulses from gamma rays with an energy of about 10.8 MeV; E _pore — the lower or upper threshold energy value, respectively, for separating gamma rays with energy that is in a predetermined range of energy values, including a value of 10.8 MeV, which in practice is preferably chosen equal to 9.2 and 11.0 MeV, respectively; U _в - a digital code corresponding to the amplitude value of electric pulses from gamma rays with energy corresponding to the energy of the maximum point of the energy spectrum due to gamma rays with an energy of about 2.23 MeV; Е _в - energy of a gamma-ray emitted by the nucleus of a hydrogen atom in interaction with a thermal neutron, Е _в = 2.23 MeV.

Then, computer 5 extracts digital codes corresponding to the amplitude value of electric pulses from gamma rays with an energy of about 10.8 MeV by comparing all digital codes corresponding to the amplitude value of electric pulses from registered gamma quanta with the obtained lower and upper threshold values for digital code corresponding to the amplitude value of electric pulses from gamma rays with an energy of about 10.8 MeV, and counts their number, determining the number of registers th e gamma rays with approximately 10.8 MeV and hence estimating the intensity of gamma radiation from a gamma-ray energy.

Then, the computer 5 compares the obtained number of registered gamma-quanta with an energy of about 10.8 MeV with the threshold value set for this quantity stored in its storage device.

If, as a result of the comparison, the number of registered gamma rays with an energy of about 10.8 MeV is less than the threshold value set for it, computer 5 issues a signal about the absence of explosive to the alarm signaling device 6, indicating it to the system operator, and sends a signal to the conveyor drive 4, starting conveyor 4, and the controlled item 1 is removed from the control, leaving the conveyor 4 from the control zone.

If, as a result of the comparison, the number of registered gamma rays with an energy of about 10.8 MeV is greater than the threshold value set for it, computer 5 gives a signal about the presence of explosive in the controlled object 1 to the alarm signaling device 6, indicating it to the system operator, and sends a signal to drive of conveyor 4, starting conveyor 4. Conveyor 4 moves the controlled object 1 from the horizontal shaft 3 of the installation 2 for neutron radiation analysis and after the release of the controlled object 1 from g horizontal shaft 3 it is removed from the conveyor belt 4 and sent for inspection.

The inventors created and implemented on a personal computer a mathematical model of an explosive detection system in a controlled subject that implements the proposed method. Studies conducted using this mathematical model confirmed the reduction in the probability of missing an explosive and false alarm when detecting an explosive using the present invention.

In particular, for example, the effect of changes in the temperature of the optoelectronic path for detecting gamma radiation from the scintillator 16 of the gamma radiation detector 11 to the analog-to-digital converter 21, inclusive, on the probability of false alarm and missed explosive when it was detected, was investigated. For example, studies have shown that a change in the temperature of gamma-ray detectors 11 of an explosive detection system that implements the known method (RU 2065156, 1996), selected for the closest analogue, from 20 to 30 ° C leads to an increase in the probability of missing an explosive from 0.01 up to 0.08 with a constant probability of false alarm equal to 0.05, or an increase in the probability of false alarm from 0.05 to 0.22 with a constant probability of missing an explosive with a value of 0.01.

However, with the same initial data, the same temperature change of the gamma-ray detectors 11 of the explosive detection system in a controlled object implemented in accordance with the present invention increases the probability of an explosive missed from 0.01 to only 0.02 with the same the value of the probability of false alarm equal to 0.05, or to increase the probability of false alarm from 0.05 to only 0.08 with a constant probability of missing an explosive equal to 0.1.

These results confirm the solution of the problem of the present invention, which consists in reducing the likelihood of missing an explosive and false alarm when detecting explosives using neutron radiation analysis.

Tests of a prototype explosive detection system in a controlled object, created in accordance with the present invention, showed the fundamental possibility of using it to detect modern nitrogen-containing explosives with a minimum mass of 100-200 g in the typical baggage of air passengers with baggage nitrogen density of nitrogen-containing materials, not being explosives, from 2.3 to 2.4 g / DM ³ . The experimentally estimated probability of correct detection of the minimum explosive was 0.95-0.97 with a false alarm probability not exceeding 0.02-0.04.

The system for detecting explosives in a controlled object showed a sufficiently high productivity of the baggage control process, providing verification of 170-190 pieces of baggage per hour. Such a performance of an explosive detection system in a controlled object can be considered acceptable even when controlling the baggage of such a large number of air passengers that wide-body airliners take on board.

Claims (7)

1. A method for detecting explosive in a controlled object, including placing a controlled object in a chamber equipped with radiation protection and at least one gamma radiation detector, irradiating the controlled object with thermal neutrons, registering the emitted gamma radiation by converting gamma rays, by at least one detector of gamma radiation into electrical pulses with amplitudes proportional to the energies of gamma rays, and comparison of amplitudes of electrical pulses with threshold values, the selection of electrical impulses with an amplitude proportional to the energy of gamma rays, which is in a predetermined range of energy values, including a value of 10.8 MeV, by comparing their amplitudes with lower and upper threshold values, counting the selected electrical impulses, deciding on the presence of explosive in a controlled object, when the number of calculated electrical impulses exceeds its threshold value, characterized in that before the placement of the controlled object, heat is irradiated With neutron chambers, the energy spectrum of the detected gamma radiation is determined, at least in the gamma-ray energy range including 2.23 MeV, and in the gamma-energy interval including the upper limit of the gamma-ray energy emitted during the interaction with thermal neutrons the nuclei of atoms of at least one chemical element that is part of the materials of the camera, radiation protection or gamma radiation detector, determine the maximum point of the energy spectrum, due to about gamma rays with an energy of about 2.23 MeV, and the point of decline of the energy spectrum in the energy range of gamma rays, including the upper limit of the energy values of gamma rays emitted during the interaction with thermal neutrons by the atomic nuclei of a given chemical element, determine the amplitudes of the electrical pulses from gamma quanta with energies corresponding to the energies of the maximum and decay points of the energy spectrum of the detected gamma radiation, ensure that the amplitudes of the electrical pulses from the gamma quantum correspond in with energies corresponding to the energies of the maximum and decay points of the energy spectrum, the calculated values, when the controlled object is irradiated with thermal neutrons, the energy spectrum of the detected gamma radiation is determined, at least in the gamma-ray energy interval including the value 2.23 MeV, the point the maximum energy spectrum due to gamma rays with an energy of about 2.23 MeV, determine the amplitude of the electrical pulses from gamma rays with an energy corresponding to the energy of the point max the energy spectrum caused by gamma quanta with an energy of about 2.23 MeV, and taking into account the specified amplitude, determine the lower and upper threshold values for the selection of electrical pulses with an amplitude proportional to the energy of gamma quanta, which is in a given range of energy values, including a value of 10 , 8 MeV, while determining the lower and upper threshold values for the extraction of electrical pulses with an amplitude proportional to the energy of gamma rays, which is in a given range of energy values, This turns the value of 10.8 MeV is carried out in accordance with the expression E = U _{pore pore} · U _in / _E, where U _pore - respectively lower or upper threshold value for the isolation of electrical pulses with an amplitude proportional to the energy of gamma rays located in a predetermined an energy range including a value of 10.8 MeV; E _pore - respectively, the lower or upper threshold energy value for the allocation of gamma rays with energy in a predetermined range of energy values, including a value of 10.8 MeV; U _in - the amplitude of the electrical pulses from gamma rays with energy corresponding to the energy of the maximum point of the energy spectrum due to gamma rays with an energy of about 2.23 MeV; Е _в - energy of a gamma-ray emitted by the nucleus of a hydrogen atom in interaction with a thermal neutron, Е _в = 2.23 MeV. 2. The method according to claim 1, characterized in that the energy spectrum of the detected gamma radiation is determined in the gamma-ray energy range, including an upper limit of 6.826 MeV, gamma-ray energy values emitted from iodine atomic nuclei interacting with thermal neutrons, included in the scintillator material of the gamma radiation detector, and determine the point of decline of the energy spectrum in the specified range of gamma-ray energy. 3. The method according to claim 1, characterized in that they determine the energy spectrum of the detected gamma radiation in the range of gamma-ray energy, including an upper limit of 4.945 MeV, gamma-ray energy values emitted during interaction with thermal neutrons by the nuclei of carbon atoms, included in the composition of the radiation protection material of the camera, and determine the point of decline of the energy spectrum in the specified energy range of gamma rays. 4. The method according to claim 1, characterized in that the energy spectrum of the detected gamma radiation is determined in the gamma-ray energy interval, including an upper limit of 8.578 MeV, gamma-ray energy values emitted during interaction with thermal neutrons by chlorine atom nuclei, included in the radiation protection material of the camera, and determine the point of decline of the energy spectrum in the specified energy range of gamma rays. 5. The method according to claim 1, characterized in that the energy spectrum of the detected gamma radiation is determined in the gamma-ray energy range, including an upper limit of 7.724 MeV, gamma-ray energy values emitted from aluminum atomic nuclei interacting with thermal neutrons, included in the structural material of the camera and the gamma-ray detector, and determine the point of decline of the energy spectrum in the specified range of gamma-ray energy. 6. The method according to any one of the preceding paragraphs, characterized in that the recession points of the energy spectrum in the energy range of gamma rays, including the upper limit of the energy values of gamma rays emitted when interacting with thermal neutrons by atomic nuclei of chemical elements that make up the chamber materials, radiation protection or gamma radiation detector, determined by numerical differentiation of the energy spectrum. 7. The method according to claim 1, characterized in that the correspondence to the calculated values of the amplitudes of the electrical pulses from gamma rays with energies corresponding to the energies of the maximum and decay points of the energy spectrum is provided by changing the transmission coefficient of the electronic path for converting gamma rays into electrical pulses and adding to electrical impulses from gamma rays of bias voltage.

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