WO2006016835A1

WO2006016835A1 - Method for detecting an explosive in an inspectable object

Info

Publication number: WO2006016835A1
Application number: PCT/RU2005/000353
Authority: WO
Inventors: Jury Iosifovich Olshansky; Aleksandr Georgievich Sorokin; Mikhail Aleksandrovich Goltsev; Andrei Borisovich Vishnevkin; Ilya Borisovich Bruk
Original assignee: Otkrytoe Aktsionernoe Obschestvo 'nauchno-Tekhnichesky Tsentr 'ratek'
Priority date: 2004-07-30
Filing date: 2005-06-16
Publication date: 2006-02-16
Also published as: RU2004124111A; RU2276352C2

Abstract

The invention relates to a material neutron-radiation analysis and can be used mainly for detecting nitrogen-containing explosive materials in closed inspected objects. The inventive method consists in exposing a chamber which is provided with a radiation shielding to thermal neutron irradiation, in recording gamma-radiation, in determining the energy spectrum of the chamber gamma-radiation within a gamma quantum energy range whose upper boundary is equal to or greater than 11 MeV, in placing the inspectable object in the chamber, in exposing said object by thermal neutron radiation and in determining the energy spectrum of the chamber gamma-radiation with said inspectable object within the same energy spectrum. The expected quantity of background gamma-quanta whose energy is about of 10.8 MeV recorded during the thermal neutron irradiation of the chamber is determined according to expression NF = NFK+ NF1 NP1/ NK1+ NF2 NP2/ NK2+ NF3(NP3/ NK3)2, wherein NFK is a quantity of the background gamma-quanta having the energy about 10.8 MeV which is specified by a cosmic component and is obtainable at a calibration stage; NF1, NF2 and NF3 are the quantities of the recorded background gamma-quantum whose energy is about of 10.8 MeV, which are obtainable on the basis of the energy of the empty chamber and are specified by the interaction of the thermal neutrons with air nitrogen atom nuclei, by the interaction of fast neutrons with iodine atom nuclei and by simultaneity of the recording of two or more low-energy gamma-quanta, respectively; NK1, NK2 and NK3 are the quantities of gamma-quanta whose energies range from 2.0 to 2.4 MeV, from 2.7 to 2.9 MeV and from 3.5 to 10.1 MeV respectively and which are registered during the irradiation of the empty chamber ; NP1, NP2 and NP3 are the quantities of gamma-quanta recorded within the same energy ranges during the irradiation of the chamber containing the inspectable object. The inventive method also consists in selecting and calculating the gamma-quanta whose energy ranges between the upper and lower energy boundary values including the 10.8 MeV value and in taking decision with respect to the presence of the explosive material when the quantity of selected gamma-quanta exceeds the guess quantity of registered background gamma-quanta. The inventive method reduces the probability the through passage of an explosive material and of a false alarm.

Description

METHOD FOR DETECTING EXPLOSIVES IN CONTROLLED SUBJECT

Technical field

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

Prior level The need to control large flows of mail or to carry out searches of hand luggage and baggage of passengers, especially in air transport, in conditions of limited time allotted for control or inspection, requires the use of methods for the detection of explosives and their technical means that do not include autopsy and visual inspection of each controlled item, but provide rapid detection of explosives with a high probability of correct of detection with a small number of errors of a false alarm.

Currently, among the many known methods for detecting explosives, methods based on the use of X-ray diffraction (Patrik Flapagap, Tespologu vs. Terror, EUSA, 1989, No 7, pp. 46-49, 51) have found practical application, which are ineffective in non-traditional form explosives and therefore allow them to be detected only in 40-60% of cases. In addition, methods of detecting explosives have found wide practical application, which are based on neutron-radiation analysis performed to determine the chemical elements that make up the explosive. Such well-known methods for detecting explosives and their installations (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 2046324, 1995, RU 2065156, 1996) 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 distribution of nitrogen concentration in a controlled subject and determined of the presence therein of the explosive upon the fact of increased nitrogen concentration.

As you know, all modern explosives contain a fairly significant 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 the nitrogen-15 atoms emit gamma rays with an energy of about 10.8 MeV. Registration and counting of such gamma-quanta 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. In this case, the determination of the presence of an increased concentration of nitrogen in the controlled object is carried out on the basis of the excess of the number of registered gamma rays of the above energy of the estimated number of registered background gamma rays.

As shown by studies of the authors of the present invention, with the exception of cosmic gamma radiation, which is quite stable, can be measured and therefore taken into account, background gamma radiation with quantum energies close to 10.8 MeV is due to the following three components. Firstly, when interacting with thermal neutrons, gamma-quanta of the indicated energy value emit nuclei of nitrogen atoms filling the chamber and the surrounding air.

Secondly, in the implementation of all of the known methods for detecting explosives based on neutron radiation analysis, registration of gamma radiation, as a rule, is performed by gamma radiation detectors, which contain a thallium activated sodium iodide scintillator and located with it a photoelectron multiplier is in the optical contact. When registering, gamma-rays emitted by a controlled object and entering the scintillator of a gamma-ray detector cause light flashes in it, whose brightness is proportional to the energies of gamma rays. 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 quanta trapped in the scintillator, which, after amplification by the amplifier, are fed to an amplitude analyzer that extracts electric pulses with an amplitude proportional to the energy of the gamma quantum. about 10.8 MeV emitted by the nucleus of a nitrogen atom.

In this case, the thermal neutron flux is formed by slowing down fast neutrons emitted by a neutron generator or a radionuclide source, for example, based on caliphornia-252. Since the deceleration to thermal energy values does not occur with all emitted fast neutrons, some fast neutrons inevitably fall into the scintillator of the gamma radiation detector, where it interacts quite intensively with the nuclei of iodine atoms, which is part of sodium iodide, with the emission of gamma quanta with energies including close to the value of 10.8 MeV. Due to the fact that in this case the source of gamma quanta with energies of the indicated values is the scintillator material itself, which, when registering gamma quanta into light flashes, practically all gamma quanta emitted by the atomic nuclei of the iodine scintillator are detected by a gamma radiation detector . Therefore, the second component of the background gamma radiation is due to the interaction of fast neutrons with the nuclei of iodine atoms.

Thirdly, since the photoelectron multiplier used in gamma-ray detectors is not a coordinate-sensitive receiver of optical radiation, its output electric signal at each moment of time is proportional to the total optical radiation flux of all light flashes occurring in the scintillator at any time. When interacting with neutrons, not only the nuclei of nitrogen atoms, but also the nuclei of atoms of many other chemical elements that make up the materials of the chamber and the controlled object, emit gamma rays with energies lower than 10.8 MeV quite intensively. With a significant number of such gamma rays, two or more gamma rays can cause two or more light flashes, which occur almost simultaneously, when registering a gamma radiation detector in the scintillator. Therefore, the output electric signal of the photomultiplier will be proportional to the total luminous flux of the optical radiation of these flashes, that is, the sum of the energy values of these two or more gamma rays. As a result of this, two or more gamma-quanta having energies significantly lower than 10.8 MeV, when their total energy is close to 10.8 MeV, while recording them simultaneously, are perceived by the gamma-ray detector as one gamma quantum with an energy of 10.8 MeV These lower-energy gamma quanta, recorded by the gamma-ray detector simultaneously as one gamma-quantum, determine the third component of the background gamma-radiation. The estimated number of detected background gamma-quanta of all three of these components is determined experimentally during preliminary calibration of the explosive detection device without placing a controlled object in it before putting it into operation. However, when using the unit for its intended purpose, due to the placement of a controlled object in the chamber, the composition of the chemical elements of the contents of which is not known, the number of recorded background gamma-quanta of the above energy varies quite significantly. This is due both to the presence in the controlled object of nitrogen-containing materials emitting such gamma quanta, which are not explosive, and to the distortion of the materials contained in it that do not contain nitrogen, the thermal neutron flux penetrating into the volume of the controlled object, as well as the fast neutron flux, scintillator reaching gamma radiation detector. In addition, the change in the estimated number of registered background gamma-quanta is due to a distortion of the energy spectrum of lower-energy gamma-quanta recorded by the gamma-ray detector simultaneously, due to gamma-radiation emitted by the atomic nuclei of the materials contained in the controlled object. Therefore, the magnitude of the background gamma radiation when irradiated with thermal neutrons of a controlled object inevitably turns out to be very significantly different from the value obtained experimentally when calibrating the installation before putting it into operation.

As a result of this, if, when an explosive is detected in a controlled object, the real background gamma radiation will be higher than the expected value of the background gamma radiation experimentally determined during calibration, the probability of false alarm will increase. With the opposite ratio of the real and estimated values of the background gamma radiation, on the contrary, the probability of an explosive missed will increase. In addition, 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 neutrons, also emit gamma radiation with gamma-ray energies of a fairly wide range of the spectrum, including energies close enough in value to 10.8 MeV. In particular, chromium nuclei emit gamma rays with an energy of 9.7 MeV, selenium with an energy of 9.9 MeV, and iron with an energy of 9.3 and 10.0 MeV. When registering gamma radiation in the process of selection emitted by the nuclei of nitrogen atoms of gamma rays with an energy that is in a predetermined interval between the lower and upper boundary energy values, including a value of 10.8 MeV, gamma rays emitted by the nuclei of chromium, selenium and iron atoms can be isolated and mistakenly recorded as gamma rays with an energy of 10.8 MeV, allegedly emitted by the nuclei of nitrogen atoms. This circumstance causes an increase in the probability of false alarm when explosives are detected.

And finally, a false alarm when detecting an explosive can be caused by genuine leather products located in the controlled object, as well as the controlled object itself, for example, a suitcase, bag, briefcase or case made of genuine leather, since genuine leather contains 10 nitrogen -15 mass percent.

Therefore, the disadvantages of all these known methods for detecting explosives based on neutron radiation analysis are the high probabilities of false alarm and missed explosives.

The closest in technical essence to the present invention should be considered a method for detecting explosives in a controlled object (RU 2206080, 2003), which includes placing the controlled object in a chamber equipped with radiation protection and at least one gamma radiation detector, irradiating the controlled object thermal neutrons, registration of emitted gamma rays, emission of gamma rays, including those with energy in a given interval between the lower and upper boundary energies and including a value of 10.8 MeV, counting the selected gamma-quanta and deciding on the presence of explosive in the controlled object when the number of gamma-quanta extracted exceeds the estimated number of registered background gamma-quanta with energy in a given energy range, including the value 10.8 MeV. 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 method of detecting explosives in a controlled object, which is the closest analogue, the decision on the presence of explosive in a controlled object is made if the number of registered gamma rays with an energy of about 10.8 MeV of the estimated number of registered background gamma rays with the same energy iey. Wherein the estimated number of registered background gamma-quanta is determined experimentally during preliminary calibration of the installation for detecting explosives without placing a controlled object in it before putting it into operation. As it was discussed in detail above, immediately upon detection of an explosive due to the placement of a controlled object in the chamber, the composition of the chemical elements of the contents of which is not known, the number of recorded background gamma-rays of the above energy varies quite significantly. This is due both to the presence in the controlled object of nitrogen-containing materials emitting such gamma quanta that are not explosive, and to the distortion of the materials contained in it that do not contain nitrogen, the thermal neutron flux penetrating into the volume of the controlled object, as well as the fast neutron flux, scintillator reaching gamma radiation detector. In addition, the change in the estimated number of registered background gamma-quanta is due to a distortion of the energy spectrum of lower-energy gamma-quanta recorded by the gamma-ray detector simultaneously, due to gamma-radiation emitted by the atomic nuclei of the materials contained in the controlled object. Therefore, the background gamma radiation inevitably turns out to be very significantly different from the value obtained experimentally when calibrating the installation before putting it into operation. As a result of this, as noted above, the likelihood of missing an explosive and false alarm when it is detected increases.

In addition, if it turns out that the controlled object contains materials consisting of such chemical elements as, for example, chromium, selenium and iron, the atomic nuclei of which, when interacting with thermal neutrons, also emit gamma radiation with gamma-ray energies quite close with a value of 10.8 MeV, when registering gamma radiation in the process of separating gamma rays emitted by the nuclei of nitrogen atoms, gamma rays emitted by the atomic nuclei of these chemical elements can be isolated and mistakenly recorded in honors gamma quanta with the energy of 10.8 MeV, allegedly emitted by nuclei of nitrogen atoms. This circumstance causes an increase in the probability of false alarm when explosives are detected. In case the controlled item, for example, a suitcase, bag, briefcase or case, is made of genuine leather or contains genuine leather products, contained in it in a significant enough amount nitrogen can also cause a false alarm, leading to an increased likelihood of a false alarm.

Therefore, the disadvantages of the method for detecting explosives in a controlled object, which is the closest analogue, as well as all of the above known methods for detecting explosives based on neutron radiation analysis, are the high probability values of false alarm and missed explosives. This circumstance is due to the fact that these methods do not include, at the stage of making a decision on the presence of an explosive, taking into account changes in background gamma radiation with a quantum energy of about 10.8 MeV, which occurs as a result of placing a controlled object in the chamber.

Disclosure of invention

An object of the present invention is to reduce the likelihood of missed explosives and false alarms when explosives are detected.

The problem is solved, according to the invention, in that a 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 thermal neutrons, registration of emitted gamma-rays, emission of gamma-rays with energy in a predetermined interval between the lower and upper boundary energy values, including the value of 10.8 MeV, the calculation of the selected gamma-quanta, the decision on the presence of explosive in the controlled object in excess of the number of allocated gamma-quanta the estimated number of registered background gamma-quanta with energy in a given range of energy values, including a value of 10.8 MeV, 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 of the camera is determined In the gamma-ray energy range with an upper limit of at least 11 MeV, when a controlled object is irradiated with thermal neutrons, the energy spectrum of the detected gamma radiation of a camera with a controlled object in the gamma-ray energy range with an upper limit of at least 11 is determined MeV, before making a decision on the basis of a change in the energy spectrum of the registered gamma radiation of a camera with a controlled object according to in relation to the energy spectrum of the detected gamma radiation of the camera, in at least one predetermined subband of gamma-ray energy, at least one correction coefficient is determined for the value of the number of detected background gamma-quanta with energy located in thermal neutrons irradiating the camera a predetermined range of energy values, including a value of 10.8 MeV, and determine the estimated number of chambers detected by thermal neutron irradiation with controlled the subject of background gamma-quanta with energy in a given energy range, including a value of 10.8 MeV, by multiplying by the correction factor obtained by irradiating the camera with thermal neutrons, the number of registered background gamma-quanta with energy in a given energy range including the value of 10.8 MeV. In this case, the correction coefficient is determined as the ratio of the numbers of gamma rays detected during irradiation of the camera with a controlled object and during the exposure of the camera and having energy values belonging to a given subrange including 2.23 MeV, as the ratio of the amounts of gamma rays irradiating the camera with a controlled object and when irradiating the camera and having energy values belonging to a given subband including a value of 2.8 MeV, and in the form of a square of the ratio of the quantities ha mmah quanta recorded upon irradiation of a camera with a controlled object and upon irradiation of a camera and having energy values belonging to a given subband of 3.5 to 10.1 MeV.

In addition, when a camera with a controlled object is irradiated, if the ratio exceeds the number of registered gamma rays with energies from 9.2 to 10.2 MeV to the number of registered gamma rays with energies from 3.4 to 7.7 MeV, the lower value increases the boundary energy value of a given energy interval, including a value of 10.8 MeV, and after increasing the lower boundary energy value of a predetermined energy interval, including a value of 10.8 MeV, if the number of selected gamma quanta exceeds the estimated number of registered background gamma rays with energy in a predetermined range of energy values, including a value of 10.8 MeV, determine the ratio of the number of selected gamma rays to the number of registered gamma rays with energies from 9.6 to 10.2 MeV and take the decision on the presence of explosive in the controlled object based on a comparison of this relationship with its two threshold values, that is, they decide on the presence of explosive when the ratio of the number of gamma rays emitted to the number of registered gamma rays with energies from 9.6 to 10 is exceeded, 2 MeV of the upper threshold value or when the lower threshold value is exceeded, the ratio of the number of selected gamma rays to the number of registered gamma rays with energies from 9.6 to 10.2 MeV is exceeded.

The thermal neutron irradiation of the camera before placing a controlled object in it together with the registration of gamma-quanta emitted by it allows you to determine the energy spectrum of the registered gamma radiation of an empty camera without a controlled object in the gamma-ray energy range with an upper limit of at least 11 MeV, and, including the background gamma radiation of an empty chamber with quantum energies of about 10.8 MeV. The determination of the energy spectrum of the detected gamma radiation of a camera with a controlled object in the energy range of gamma quanta with an upper limit of at least 11 MeV when irradiating a controlled object with thermal neutrons then allows, based on a comparative analysis, in at least one given energy subband gamma rays of the obtained energy spectra of the registered gamma radiation of an empty camera and a camera with a controlled object placed in it before deciding It is possible to determine at least one correction factor for the value of the number of detected background gamma quanta with energy in a given energy range including 10.8 MeV obtained by thermal neutron irradiation of the camera, and therefore evaluate the change in background gamma radiation with quantum energies of about 10.8 MeV, due to the presence in the chamber of a controlled object. Then this allows, before making a decision, to partially take into account the change in background gamma radiation with quantum energies of about 10.8 MeV due to the presence of a controlled object in the chamber, and more accurately determine the estimated number of background gamma quanta with energy controlled by neutron irradiation with a controlled object. , which is in a predetermined range of energy values, including a value of 10.8 MeV, by multiplying by the correction factor obtained by irradiation with thermal ronami chamber value for the number of background gamma rays with an energy which is in a predetermined range of energy values, including a value of 10.8 MeV. Such accounting for changes in the background gamma radiation and, therefore, a more accurate determination of the estimated number of background gamma-quanta recorded with thermal neutrons irradiating a controlled object, with energies in a given energy range including a value of 10.8 MeV, reduces the decision probabilities of false alarm and missed explosives. This statement is confirmed by the following considerations.

As noted above, one of the most significant components of background gamma radiation with a quantum energy of about 10.8 MeV is due to the interaction of thermal neutrons with the nuclei of nitrogen atoms in the air that fills the chamber and surrounds it. Placing the controlled object in the chamber causes distortion of the thermal neutron flux in the materials that do not contain nitrogen in it. Experimental studies have shown that the presence in the materials of a controlled object, for example, 500 g of chlorine, which is often found in materials contained, for example, in baggage and hand luggage of air passengers, reduces the thermal neutron flux by about 1.5 times and therefore causes the corresponding a decrease in the specified component of the background gamma radiation with a quantum energy of about 10.8 MeV compared with this component for an empty chamber. In such a situation, when deciding whether or not an explosive is used, the value of background gamma radiation with an energy of about 10.8 MeV, obtained as a result of calibrating the device without placing a controlled object in the chamber, leads to unreasonably overestimating the estimated number of cameras detected during irradiation with thermal neutrons with a controlled subject of background gamma-quanta with energy in a predetermined range of energy values, including a value of 10.8 MeV, and can lead to skip explosive. This is also due to the fact that a decrease in the thermal neutron flux by the contents of a controlled object will lead to a corresponding decrease in the number of 10.8 MeV gamma rays emitted by the nuclei of nitrogen atoms of an explosive in a controlled object.

A significant amount of boron polyethylene is used as a material for the radiation protection of the chamber, since it effectively absorbs neutrons. At the same time, the composition of polyethylene includes hydrogen, whose nuclei of atoms as a result of interaction with neutrons are intensely emit gamma radiation with gamma-ray energies of about 2.23 MeV, which leads to the appearance in the energy spectrum of gamma radiation, both an empty camera and a camera with a controlled object, a pronounced maximum in the gamma-ray energy interval, including the value 2, 23 MeV, near the specified value of the energy of gamma rays. The intensity of gamma radiation with quantum energies of the indicated value also substantially depends on the magnitude of the thermal neutron flux.

Therefore, the authors of the present invention proposed to evaluate the change in the flux of thermal neutrons under the influence of the contents of the controlled object and take into account the effect of this change on one of the components of the background gamma radiation with a quantum energy of about 10.8 MeV, due to the interaction of thermal neutrons with the nuclei of nitrogen atoms filling the chamber and the surrounding its air, based on the analysis of changes in the energy spectrum of the registered gamma radiation of a camera with a controlled object in relation to energy the spectrum of the detected gamma radiation of an empty chamber in a given subband of gamma-ray energy, including a value of 2.23 MeV. To this end, according to the present invention, a correction coefficient is determined in the form of the ratio of the gamma-quanta detected by irradiating a camera with a controlled object and irradiating an empty chamber and having energy values belonging to a given subband including a value of 2.23 MeV. Then, the estimated number of cameras with a controlled object of background gamma-quanta with energy located in a given range of values, determined by a given component of background gamma radiation, is determined

, energy, including the value of 10.8 MeV, by multiplying by the obtained correction coefficient obtained by irradiation with thermal neutrons of the empty chamber due to this component, the value of the number of registered background gamma-quanta with energy in a given range of energy values, including the value of 10.8 MeV.

As noted above, the second most important component of background gamma radiation with a quantum energy of about 10.8 MeV is due to the interaction of fast neutrons, which have not undergone slowdown to thermal energy values, with the nuclei of iodine atoms, which are part of the sodium iodide scintillator of the gamma radiation detector . Placing the controlled object in the chamber causes a distortion of the fast neutron flux in the materials due to their deceleration or capture. Experimental studies have shown that the presence in the materials of a controlled object, for example, 1 kg of water, carbon or polyethylene, reduces the fast neutron flux by 30-50% and therefore causes a corresponding decrease in the indicated component of background gamma radiation with a quantum energy of about 10.8 MeV compared with this component for an empty camera. In this case, when using the decision on the presence or absence of an explosive, the use of background gamma radiation with an energy of about 10.8 MeV, obtained as a result of calibrating the installation without placing a controlled object in the chamber, leads to unreasonably overestimating the number of cameras detected during irradiation with thermal neutrons with a controlled subject of background gamma-quanta with energy located in a given range of energy values, including a value of 10.8 MeV, and can lead to Omitting explosive. At the same time, it was experimentally established by the authors of the present invention that the vast majority of chemical elements that make up the materials contained in the controlled object, in the range of gamma-ray energies close to 2.8 MeV, practically do not distort the energy spectrum of emitted gamma radiation directly due to neutron capture. To a greater or lesser extent, most chemical elements only cause slowing down of fast neutrons, which ultimately leads to a decrease in the second of these components of background gamma radiation with a quantum energy of about 10.8 MeV, which is due to the interaction of fast neutrons with the nuclei of iodine atoms included in composition of sodium iodide scintillator gamma radiation detector.

Therefore, the authors proposed to evaluate the change in the fast neutron flux under the influence of the contents of the controlled object and take into account the effect of this change on the second component of background gamma radiation with a quantum energy of about 10.8 MeV, due to the interaction of fast neutrons with the nuclei of the iodine atoms of the scintillator of the gamma radiation detector, on based on the analysis of changes in the energy spectrum of the registered gamma radiation of a camera with a controlled object in relation to the energy spectrum vannogo gamma empty chamber in a predetermined subband energy gamma-rays, comprising a value of 2.8 MeV. To this end, according to the present invention, a correction coefficient is determined in the form of the ratio of the amounts of gamma rays detected by irradiating a camera with a controlled object and irradiating the chamber and having energy values belonging to a given subband including a value of 2.8 MeV. Then, the estimated number of background gamma-quanta cameras with a controlled subject of background gamma-quanta with energy located in a predetermined energy range including 10.8 MeV, determined by this component of the background gamma radiation, is determined by multiplying by the obtained correction coefficient obtained by irradiation thermal neutrons of the chamber due to this component, the value of the number of registered background gamma rays with energy, finding scheysya in a predetermined range of energy values comprising the value of 10.8 MeV.

As discussed above, the third of the most significant components of the background gamma radiation with an energy of about 10.8 MeV is due to two or more gamma rays detected simultaneously, which have energies significantly lower than 10.8 MeV, but whose total energy is close to this value . While recording them simultaneously, the gamma-ray detector perceives such gamma-rays as one gamma-ray with an energy of about 10.8 MeV. Placing a controlled object in the chamber causes a distortion of the energy spectrum of such gamma rays due to gamma radiation emitted by the nuclei of atoms contained in the controlled object materials. The experiments showed that the presence in the controlled object of materials containing iron, titanium, chromium or chlorine in an amount of 500 g causes an increase in this component of the background gamma radiation with an energy of about 10.8 MeV, respectively, 4.4, 17, 2.2 and 6.5 times.

To take into account the distortion by materials of a controlled object of the indicated component of the background gamma radiation with an energy of about 10.8 MeV, the authors of the present invention proposed to analyze the change in the energy spectrum of the registered gamma radiation of a camera with a controlled object with respect to the energy spectrum of an empty camera in the gamma-ray energy subband from 3.5 to 10.1 MeV, that is, in that subband. which accounts for the energies of gamma rays, which, if detected simultaneously, give the output signal of a gamma radiation detector corresponding to one gamma quantum with an energy of about 10.8 MeV. Since it was found that the number of coincidences in the time of registration of gamma rays varies in direct proportion to the square of the number of source gamma rays, the correction factor for this of the background gamma radiation component, it was proposed to determine in the form of a square the ratios of the amounts of gamma quanta detected during irradiation of a camera with a controlled object and during irradiation of an empty camera and having energy values belonging to a given subband of 3.5 to 10.1 MeV. And then determine the estimated number of background gamma quanta with an energy in the specified range of energy values including 10.8 MeV due to this component of the background gamma radiation detected by thermal neutron irradiation by multiplying by the correction coefficient obtained at thermal neutron irradiation of an empty chamber due to this component, the value of the number of registered background gamma rays with energy it, which is in a predetermined range of energy values, including a value of 10.8 MeV.

As a result, the estimated number of registered background gamma-quanta with energy in a predetermined range of energy values, including a value of 10.8 MeV, is determined in the form, for example, of the sum of the three indicated components of the background gamma radiation obtained after multiplication by the corresponding correction factor.

In addition, an increase in the lower boundary energy value of a given energy interval, including a value of 10.8 MeV, if the threshold value is exceeded by the ratio of the number of gamma quanta recorded with radiation from a camera with a controlled object with energies from 9.2 to 10.2 MeV to the number of registered gamma rays with energies from 3.4 to 7.7 MeV additionally reduces the likelihood of false alarms when explosives are detected. This is confirmed by the following circumstances.

As noted above, since the 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 neutrons also emit gamma radiation with gamma-ray energies of a fairly wide range of the spectrum, including with energies quite close in value to 10.8 MeV. When registering gamma radiation during the emission of gamma quanta emitted by the nuclei of nitrogen atoms with energies in the specified interval between the lower and upper boundary energy values, including 10.8 MeV, gamma quanta emitted by the nuclei of chromium, selenium and iron atoms, can be isolated and mistakenly recorded as gamma rays with an energy of 10.8 MeV, supposedly emitted by the nuclei of nitrogen atoms. In particular, it was experimentally established that when the interval between the lower and upper boundary energy values equal to 9.9 and 11.0 MeV, respectively, is selected for the selection of gamma rays by the inventors, the same number of selected gamma rays falling into the indicated interval is the same as extracted gamma rays from 100 g of explosive nitrogen give, for example, 75 g of chromium emitting gamma rays with an energy of about 9.7 MeV, 30 g of selenium emitting gamma rays with an energy of about 9.9 MeV, or 4 kg iron emitting gamma qua you with energies of about 9.3 and 10.0 MeV. Therefore, the presence in a controlled object of materials containing similar chemical elements causes a significant increase in the likelihood of false alarm when explosives are detected.

At the same time, it was experimentally established by the inventors that, in the absence of a significant amount in the controlled object, leading to an erroneous decision to detect explosives, materials containing chromium, selenium or iron, the ratio of the number of gamma- quanta with energies from 9.2 to 10.2 MeV to the number of registered gamma rays with energies from 3.4 to 7.7 MeV lies in the range 0.0002-0.0006. If there are materials in the controlled object containing the indicated chemical elements, this ratio increases. So, for example, when the content of the controlled object contains 75 g of chromium, this ratio is already 0.001.

Therefore, it was proposed at the stage of detection of explosives to establish the presence of materials in a controlled object containing a significant amount of chromium, selenium or iron, to determine the specified ratio of the number of registered gamma rays and, if they exceed a threshold value, increase the lower boundary energy value of a given energy range including a value of 10.8 MeV, which prevents the emission of gamma rays emitted by the indicated chemical elements and therefore reduces the probability st false alarm.

An additional determination after increasing the lower boundary energy value of a given energy range, including a value of 10.8 MeV, if the number of extracted gamma-quanta exceeds the expected number of registered background gamma-quanta with energy in a predetermined energy range, including a value of 10.8 MeV , related to the number of allocated gamma m a registered gamma-quanta with energies from 9.6 to 10.2 MeV and making a decision on the presence of explosive in a controlled object based on a comparison of this relationship with its two threshold values, that is, making a decision on the presence of explosive when the ratio exceeds the amount of gamma quanta to the number of registered gamma quanta with energies from 9.6 to 10.2 MeV of the upper threshold value or when the lower threshold value exceeds the ratio of the number of selected gamma quanta to the number of registered gamma rays with energies from 9.6 to 10.2 MeV also reduces the likelihood of false alarm that a controlled object made of genuine leather can cause, for example, a suitcase, bag, briefcase or case, or products made from natural skin thanks to the nitrogen contained in natural skin. This is confirmed by the following circumstances. As noted above, genuine leather contains a fairly significant amount of nitrogen, amounting to 10-15 mass percent. When interacting with thermal neutrons, the nuclei of nitrogen atoms contained in natural skin emit gamma rays with an energy of about 10.8 MeV, as a result of registration of which an erroneous decision can be made about the presence of explosives, that is, a false alarm error is made.

At the same time, genuine leather products contain about 3-5 mass percent of chromium, since chromium-containing substances are used for leather dressing. The authors of the present invention experimentally established that when irradiated with thermal neutrons of various products made of genuine leather, the ratio of the number of detected gamma rays with an energy of about 10.8 MeV emitted by the nuclei of nitrogen atoms, to the number of registered gamma rays with an energy of about 9.7 MeV, emitted by the nuclei of chromium atoms, remains almost the same and lies in the range of 0.6-0.9.

Therefore, the authors proposed at the decision-making stage if the number of gamma-rays emitted exceeds the expected number of registered background gamma-quanta with energies in a given energy range, including 10.8 MeV, in which a decision should be made on the presence of explosive substances, carry out an additional check if a significant number of registered gamma-quanta with an energy of about 10.8 MeV are connected with the presence of a non-explosive substance in a controlled object substances, and products made of genuine leather. Such a check becomes possible only after increasing the lower boundary energy value of a given energy range for gamma-ray emission, including a value of 10.8 MeV, to a value exceeding the energy of about 9.7 MeV of gamma-ray chromium atoms emitted by nuclei and equal to, for example, 10.2 MeV. To do this, determine the ratio of the number of selected gamma rays with an energy of about 10.8 MeV to the number of registered gamma rays with energies in the range from 9.6 to 10.2 MeV, which contains the energy of gamma rays emitted by the nuclei of chromium atoms, and decide on the presence of an explosive in a controlled subject based on a comparison of this relationship with its two threshold values. In the case when there is no explosive in the controlled object, but genuine leather products are contained, this ratio is in the range of 0.6-0.9 and, as a result of its comparison with two threshold values, they decide on the absence of explosive. In the case when the specified ratio exceeds the upper threshold value equal to, for example, 0.9, a decision is made on the presence of an explosive in a controlled object, since such a situation arises when there are other than explosive, genuine leather products or other materials in the controlled object low in chromium. In the case when the indicated ratio is less than the lower threshold value equal to, for example, 0.6, they also decide on the presence of an explosive in a controlled object, since this situation occurs when there are materials with a significant chromium content in the controlled object, in addition to the explosive . This provides an additional reduction in the likelihood of false alarm that genuine leather products can cause.

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

In accordance with the present invention, 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 by converting gamma rays, at least one detector of gamma radiation into electrical pulses with amplitudes proportional to the energies of gamma quanta, and comparing the amplitudes of the electrical pulses with threshold values; determine the energy spectrum of the registered gamma radiation of an empty chamber in the energy range of gamma rays with an upper boundary of at least 11 MeV. In practice, it is preferable to determine the energy spectrum in the range of energy values from 1 to 13

MeV; on the basis of the obtained energy spectrum of the registered gamma radiation of an empty camera, the number of registered background gamma-quanta with energy lying in a predetermined interval between the lower and upper boundary energy values including the value of 10.8 MeV is counted. In practice, the number of such registered background gamma-quanta is calculated in two intervals of energy values from 9.9 to 11.0 MeV and from 10.2 to 11, 0 MeV and for each energy interval the quantities N _Ф1 , N _ф2 , N _фз registered background gamma rays corresponding to the three abovementioned components of the background gamma radiation, due respectively to the emission of gamma rays by nitrogen in the air, the interaction of fast neutrons with nuclei of iodine atoms and the simultaneous detection of two or more gamma rays of lower energy ; on the basis of the obtained energy spectrum of the registered gamma radiation of an empty chamber, the number Nki of registered gamma quanta with energy having values belonging to a given subband including a value of 2.23 MeV is calculated. In practice, it is preferable to select a given sub-range from 2.0 to 2.4 MeV; on the basis of the obtained energy spectrum of the registered gamma radiation of an empty camera, the number Nkg of registered gamma-quanta with energy having values belonging to a given subband including a value of 2.8 MeV is calculated. In practice, it is preferable to select a given sub-range from 2.7 to 2.9 MeV; on the basis of the obtained energy spectrum of the registered gamma radiation of an empty camera, the number N _K s of registered gamma-quanta with energy having values belonging to a given subband of 3.5 to 10.1 MeV is counted; then placed in a chamber equipped with radiation protection and, by at least one gamma-ray detector, controlled object;

- irradiated with thermal neutrons with an energy of about 0.025 eV, a controlled object located in the chamber;

- register gamma radiation by converting gamma rays by at least one gamma radiation detector into electrical pulses with amplitudes proportional to the energies of gamma rays and comparing the amplitudes of the electrical pulses with threshold values; determine the energy spectrum of the registered gamma radiation of a camera with a controlled object in it in the gamma-ray energy range with an upper limit of at least 11 MeV. In practice, it is preferable to determine the energy spectrum in the range of energy values from 1 to 13 MeV;

- based on the obtained energy spectrum of the registered gamma radiation of a camera with a controlled object in it, the number N _{m of} registered gamma-quanta with energy having values belonging to a given subband including a value of 2.23 MeV is counted. In practice, it is preferable to select this sub-range from 2.0 to 2.4 MeV. The first correction factor is determined as the ratio of the numbers of gamma rays detected when the camera with the controlled object was irradiated and when the empty camera was irradiated and having energy values belonging to a given subband including 2.23 MeV, in the form ki = N _m / Nκi;

- based on the obtained energy spectrum of the registered gamma radiation of a camera with a controlled object located in it, the number N _{P2 of} registered gamma-quanta with energy having values belonging to a given subband including a value of 2.8 MeV is counted. In practice, it is preferable to select this sub-range from 2.7 to 2.9 MeV. The second correction factor is determined as the ratio of the number of gamma quanta recorded when the camera with the controlled object was irradiated and when the empty camera was irradiated and having energy values belonging to a given subband including a value of 2.8 MeV, in the form k ₂ ⁼ Nпг / Nкг;

- on the basis of the obtained energy spectrum of the registered gamma radiation of a camera with a controlled object in it, the number N _{pz of} registered gamma quanta with energy having values belonging to a given subband of 3.5 to 10.1 MeV is counted. The third correction factor is determined as the squared ratio of quantities gamma rays detected by irradiating a camera with a controlled object and by irradiating an empty chamber and having energy values belonging to a given subrange of 3.5 to 10.1 MeV, in the form k ₃ = (N _P s /

Nκ) ² ; - based on the obtained energy spectrum of the registered gamma radiation of a camera with a controlled object in it, the number of registered gamma rays with energies from 9.2 to 10.2 MeV and the number of registered gamma rays with energies from 3.4 to 7.7 are calculated MeV, determine their ratio and compare the resulting ratio with a threshold value equal to, for example, 0.0007. If the obtained ratio exceeds the specified threshold value, for example, the lower boundary energy value of the specified energy range, including 10.8 MeV, for example, from 9.9 to 10.2 MeV, is increased, for example, by 3%, thereby narrowing the specified interval from the values 9.9-1 1.0 MeV to 10.2-11.0 MeV;

- determine the estimated number of recorded gamma-ray photons detected by thermal neutron irradiation of a camera with a controlled object with energy in a predetermined energy range including a value of 10.8 MeV, in accordance with the expression

where N _Ф1 , N ф2 ₎ Nψ ₃ - obtained at the stage of analysis of the energy spectrum of an empty chamber, corresponding to the three above-mentioned background components of the number of registered background gamma-quanta with energies in the range from 9.9 to 11.0 MeV or from 10.2 to 1 1,0 MeV, selected depending on the result of the comparison performed in the previous step; N _ФК - obtained at the stage of calibration of the system for detecting explosives in a controlled object before putting it into operation, the number of background gamma-quanta due to the cosmic component with energies in the range of 9.9-11, 0 MeV or 10.2-11, 0 MeV, selected depending on the result of the comparison performed in the previous step; - select gamma quanta with energy that is in a predetermined interval between the lower and upper boundary energy values, including the value of 10.8 MeV, and count their number N. In this case, gamma quanta with energy in the range of 9.9-11, 0 MeV or 10.2-11, 0 MeV, selected depending on the result performed before the previous comparison step; - to compare the number N of selected gamma rays with the obtained estimated number N _{f of} registered background gamma rays with energy in a given range of energy values, including a value of 10.8 MeV, determine the logarithm of the likelihood ratio, for example, of the following form L = (N In (1 + N _o / Nф) -N _o ), where N is the number of selected gamma-quanta with energy in a given interval between lower and upper boundary energy values, including a value of 10.8 MeV; N ₀ - obtained experimentally during preliminary calibration, the number of gamma-quanta detected with a minimum detectable mass of gamma-quanta with energy in a given interval between the lower and upper boundary energy values, including a value of 10.8 MeV, recorded in the case of a nitrogen-containing explosive in a controlled object; N _f - the estimated number of registered background gamma rays with energy in a predetermined range of energy values, including a value of 10.8 MeV; comparing the obtained logarithm L of the likelihood ratio with the lower and upper threshold values equal respectively to L ₁ = In (O - Ppo) / (1-Plt)) and L ₂ = ln (Ppo / Plt) _> where P _P o is the required probability of correct explosive detection in a controlled subject; P _L t is the required probability of false alarm .. If, as a result of comparing the logarithm L, the likelihood ratios are less than the lower threshold value L ₁ (L <l_i), a decision is made on the absence of explosive and the controlled object is removed from the camera and removed from the control. If the value of the logarithm of the likelihood ratio lies between the lower and upper threshold values L ₁ and L ₂ (L ₁ <L <L ₂ ), a decision on the presence or absence of explosives with the required probabilities of correct detection and false alarm cannot be made. In this case, control is continued by conducting repeated neutron-radiation analysis of the controlled object with repeated irradiation with thermal neutrons, registration of gamma radiation and re-decision, as provided by the proposed method; when the logarithm of L exceeds the likelihood ratio of the upper threshold value L ₂ set for it (L> L ₂ ) if gamma-quanta with energy located in a specified interval between the lower and upper boundary energy values including the value of 10.8 MeV are selected, was carried out in a wider energy range from 9.9 to 11.0 MeV, they decide on the presence of explosives in the controlled object; when the logarithm of L exceeds the likelihood ratio of the upper threshold value L ₂ set for it (L> L ₂ ) if gamma quanta with energies in a given interval between the lower and upper boundary energy values, including a value of 10.8 MeV, were extracted in a narrower energy range from 10.2 to 11.0 MeV, the ratio of the number N of gamma quanta to the number of registered gamma quanta with energies in the range from 9.6 to 10.2 MeV and decide on the presence of an explosive in a controlled object based on a comparison of this ratio with its two threshold values. When the specified ratio exceeds the upper threshold value equal to, for example, 0.9, or when the specified ratio is less than the lower threshold value equal to, for example, 0.6, a decision is made on the presence of explosives in the controlled object.

Then the controlled object is removed from the chamber and in the case of a decision on the presence of explosive in it, 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.

In FIG. 1 shows a system for detecting explosives in a controlled object that implements the inventive method, where 1 is a controlled object, 2 is a facility for neutron radiation analysis, 3

- horizontal shaft, 4 - conveyor, 5 - computer and 6 - alarm.

In FIG. 2 shows a longitudinal section along AA of the installation 2 for neutron radiation analysis (Fig. 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 the side reflector neutrons and 13 is the lower neutron reflector.

In FIG. 3 shows a longitudinal section of a gamma-ray detector 11, where 14 is a detector housing, 15 is a neutron filter cup, 16 is a scintillator and 17 is a photomultiplier.

In FIG. 4 is a structural diagram of the electronic equipment included in the installation 2 for neutron-radiation analysis, where 18 is an amplifier and 19 is an analog-to-digital converter.

In FIG. 5 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 camera with radiation protection and gamma radiation detectors, but without a controlled object and recorded for 1,000 s, where the number of registered gamma rays is given along the ordinate axis in a logarithmic scale.

In FIG. 6 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 gamma radiation detectors and recorded for 1000 s, where the number of registered gamma quanta is given along the ordinate axis on a logarithmic scale.

In FIG. 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 containing about 200 g of nitrogen-containing explosive and a camera with radiation protection and gamma radiation detectors and recorded for 1000 s, where the number of registered gamma rays is given along the ordinate axis in a logarithmic scale.

In FIG. 8 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, but containing 75 g of chromium, and a camera with radiation protection and gamma radiation detectors and recorded for 1000 s, where the number of registered gamma rays is given along the ordinate axis on a logarithmic scale.

The best embodiment of the invention

Implementing the inventive method, a system for detecting explosives in a controlled object contains (Fig. 1) installation 2 for neutron radiation analysis passing through the horizontal shaft 3 of installation 2 for neutron radiation analysis, conveyor 4, computer 5 with alarm 6, and electronic equipment, 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 (Fig. 2) a housing 7, inside of which there is 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 s passes through housing 7 and radiation protection 8 a conveyor belt 4 located along it in its lower part 4. In the central part of the horizontal shaft 3 there is a chamber 9 formed by two side neutron reflectors 12 and a lower neutron reflector 13 and designed to accommodate the controlled object 1 when it is 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 mounted 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 throughout the volume of the controlled object 1. Above the camera 9 in a radiation the protection of the 8th cavity is equipped with a thermal neutron emitter 10, which is made in the form of a radionuclide source of fast neutrons • based on caliphoria-252 with the possibility of leduyuschego polyethylene slowing down to thermal energies of about 0.025 eV and is similar in design thermal neutron radiator used in implementing one of the known methods (RU 2065156, 1996). In the cavity 8 made in the radiation protection under the chamber 9, gamma radiation detectors 11 are installed behind the lower neutron reflector 13. To ensure the possibility of stopping the conveyor belt 4, when the controlled object 1 along the horizontal shaft 3 enters the chamber 9, 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 optical radiation receiver and not shown in the figures.

The gamma-ray detector 11 (Fig. 3) comprises an aluminum detector body 14 made with an aluminum photomultiplier 17 located in its optical contact with a scintillator 16. The inorganic scintillator based on it is most preferably used as a scintillator 16. thallium activated sodium iodide. To reduce the effect 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 series-connected photoelectronic multiplier 17 of the gamma radiation detector 11, an amplifier 18 and an analog-to-digital converter 19, the output of which is connected to the input of the computer 5. In addition, the outputs of the computer 5 are connected to the input of the alarm signaling device 6, intended for generating signals of the presence or absence of explosive in the controlled object 1, as well as with the drive of the conveyor 4 for supplying start and stop signals of the conveyor 4, which is not shown in the figures.

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

Initially, an empty chamber 9 is irradiated with thermal neutrons without placing a controlled object 1 in it to obtain the energy spectrum of its gamma radiation. To do this, open the flap of the thermal neutron emitter 10 (not shown in the figures), which emits thermal neutrons with an energy of about 0.025 eV into the internal cavity of the chamber 9. When irradiated with thermal neutrons of the chamber 9, radiation protection 8, gamma radiation detectors 11 and other units of installation 2 for of neutron-radiation analysis, radiative capture of thermal neutrons by atomic nuclei of chemical elements that make up the materials used in them, as well as air nitrogen, occurs, as a result of which these atomic nuclei pass excited 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.

Some of these gamma quanta fall into the scintillators 16 of the gamma radiation detectors 11 (Fig. 3) and cause light flashes in them, the brightness of which is proportional to the energies of the gamma rays incident. 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 amplifier 18 (Fig. 4), electrical pulses from gamma rays are fed to an analog-to-digital converter 19, which converts the amplitude value of each electric pulse from gamma rays to a digital code that is input into computer 5. Computer 5, by comparing with the threshold values of the received digital codes corresponding to the amplitude values of the electrical pulses from gamma quanta and therefore 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 up to 13 MeV, according to the value of its energy, each registered gamma-quantum belongs to, and counts and remembers the number of gamma-quanta recorded over a period of 5-10 minutes that have an energy value within each th 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 on their prototype system for detecting explosives in a controlled object for a time of 1000 s is shown in FIG. 5, where the number of registered gamma rays along the ordinate axis is given on a logarithmic scale. The maximum energy spectrum of gamma rays of about 2.23 MeV is clearly visible in the energy spectrum of gamma radiation, which is due to gamma rays emitted by the nuclei of hydrogen atoms that make up the radiation protection material 8.

Based on the obtained energy spectrum of the detected gamma radiation of an empty camera 9, computer 5 determines the number of registered background gamma quanta with energy in a predetermined interval between the lower and upper boundary energy values, including a value of 10.8 MeV. In practice, the number of such registered background gamma rays is determined by computer 5 in two intervals from 9.9 to 11.0 MeV and from 10.2 to 11.0 MeV. In this case, computer 5 determines and stores for each of these two energy intervals the amounts of N ₀₁ , N ₀₂ , N ₀₃ registered gamma rays corresponding to the three abovementioned components of the background gamma radiation, due respectively to the emission of gamma rays by nitrogen by the air, the interaction of fast neutrons with nuclei of iodine atoms and the simultaneous registration of two or more gamma rays. In this case, the computer 5 determines the indicated number of background gamma-quanta recorded over the same time interval as the time interval registration of gamma rays upon irradiation by neutrons of a controlled object 1, that is, as noted below, in 5-10 seconds.

For a more accurate determination of these three components of the background gamma radiation, this operation is preferably carried out at the stage of calibration of the system for detecting explosives in a controlled object before putting it into operation. The authors of the present invention have developed a method for determining at the calibration stage these three components of the background gamma radiation, as well as the number N _{FK of} background gamma rays due to the cosmic component, which is implemented in a prototype system for detecting explosives in a controlled object.

In accordance with this technique, initially the number Nk of background gamma-quanta determined by the cosmic component is determined by detecting gamma radiation by detectors 11 and counting 5 gamma-quanta with energies from 9.9 to 11.0 MeV and from 10.2 to 11 by a computer , 0 MeV in conditions when a thermal neutron emitter 10 is not installed on the installation 2 for neutron radiation analysis.

Then determine the number N _{ph1 of} background gamma rays with energies from 9.9 to 11, 0 MeV and from 10.2 to 11, 0 MeV, due to the nitrogen of the air in the chamber 9. To do this, sequentially placed at different points in the chamber 9 by over its entire volume, reference material with a given known mass value of the nitrogen contained in it, irradiate it with thermal neutrons from a calitronium-252 thermal neutron emitter 10, register gamma quanta with the indicated energy values by gamma radiation detectors 11 and calculate their number by computer 5 Then, for each elementary volume of the chamber 9 having given dimensions and located at each placement point of this reference material, taking into account the known mass of nitrogen contained in the air of this elementary volume, computer 5 based on the number of calculated gamma-quanta in accordance with a direct proportional dependence calculates the number of background gamma rays of the above energies due to air nitrogen contained in each elementary volume of chamber 9. As a result of the summation by computer 5 of all the amounts of background gamma-quanta obtained for each elementary volume of chamber 9, the number N _ph -i of background gamma-quanta with energies from 9.9 to 11.0 MeV and from 10.2 to 11.0 is calculated MeV, caused by nitrogen in the air chamber 9. To determine the number of N _{phz of} background gamma-quanta due to the simultaneous detection of two or more gamma-quanta of lower energies, a radionuclide emitter 10 of thermal neutrons is removed from installation 2 for neutron radiation analysis and a neutron generator is installed as a radiator of 10 thermal neutrons, the principle of which based on deuterium-deuterium reaction. Such a neutron generator emits a stream of monochromatic fast neutrons with an energy of about 2.5 MeV, which are then decelerated to thermal energy values and, after deceleration, are used to irradiate the chamber 9. The indicated value of fast neutron energy in this case is not enough to ensure that when they interact with nuclei scintillator iodine atoms 16 of the gamma radiation detector 11, these nuclei emitted gamma rays with an energy of about 10.8 MeV. Therefore, when the chamber is irradiated with 9 neutrons using a neutron generator, the component of the background gamma radiation due to the interaction of fast neutrons with the nuclei of iodine atoms is absent. After registering background gamma-rays with energies from 9.9 to 11, 0 MeV and from 10.2 to 11, 0 MeV and calculating their number, computer 5, in accordance with the specified method, subtracts values from the calculated number of background gamma-quanta earlier the obtained amount of N _f k of background gamma-rays due to the cosmic component and the number of N _{f1 of} background gamma-rays due to air nitrogen, resulting in the number N _{fz of} background gamma-rays due to the simultaneous registration of two or more gamma-quanta of lower energy th.

To determine the amount of Nph _{2 of} background gamma-rays due to the interaction of fast neutrons with the nuclei of iodine atoms, a radionuclide emitter 10 of thermal neutrons is reinstalled at installation 2 for neutron radiation analysis, camera 9 is irradiated with thermal neutrons, and background gamma-quanta with energies from 9 are recorded , 9 to 11, 0 MeV and from 10.2 to 11, 0 MeV and calculate their number by computer 5. Next, computer 5 from the obtained number of registered background r-quanta recorded in this case subtracts the values previously obtained x the number N _{ФК of} background gamma-rays due to the cosmic component, the number N _{Ф1 of} background gamma-rays due to air nitrogen, the number N _{fz of} background gamma-rays due to the simultaneous detection of two or more gamma-rays of lower energies, resulting in the number N _{f2 of} background gamma rays due to the interaction of fast neutrons with the nuclei of iodine atoms.

For created prototype explosive detection system substances in a controlled subject by the inventors, in accordance with the indicated procedure, were experimentally obtained for each of these two energy intervals the amounts of N _Ф1 , N _ф2 , N _ф3 registered background gamma-quanta, corresponding to the three above-mentioned components of the background gamma radiation, caused respectively by emission of gamma quanta by air nitrogen, the interaction of fast neutrons with the nuclei of iodine atoms, and the simultaneous registration of two or more gamma quanta of lower energies. So, for example, for the gamma-ray energy interval from 9.9 to 11.0 MeV during the registration time equal to 100 s, they amounted to 40, 59, and 51 gamma-quanta, respectively. For this prototype of an explosive detection system in a controlled object, the inventors experimentally obtained in accordance with the above methodology that in the range of gamma-ray energies of 9.9-11.0 MeV the number of background gamma-quanta due to the cosmic component over time registration 100 s is 10.

Then, on the basis of the obtained energy spectrum of the registered gamma radiation of an empty camera, computer 5 determines and stores the number N _K i of registered gamma rays with energies from 2.0 to 2.4 MeV, the number N « ₂ registered gamma rays with energies from 2, 7 to 2.9 MeV and N _K s of registered gamma rays with energies from 3.5 to 10.1 MeV. In this case, the computer 5 determines the indicated number of gamma rays recorded over the same time interval as the time interval for registering gamma rays when neutrons are irradiated by the controlled object 1, that is, as noted below, in 5-10 seconds. As a result of this, 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 neutron radiation analysis unit 2, the conveyor belt will be stopped by a signal from a stop sensor not shown in the figures 4 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 irradiate, including a controlled object 1. When irradiated with thermal neutrons of a controlled object 1, chamber 9, radiation protection 8, gamma radiation detectors 11 and others elements of installation 2 for neutron radiation The analysis involves the radiative capture of thermal neutrons by the atomic nuclei of the chemical elements that make up the materials contained in them, 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 particular, when thermal neutrons are irradiated, including nitrogen-containing materials located in the controlled object 1, radiation capture of thermal neutrons by the 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 of the nuclei of nitrogen-15 atoms from the excited state 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.

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 received in 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 belongs to 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 using the created prototype of an explosive detection system in a controlled object during 1000 s, when the controlled object 1 does not contain nitrogen-containing explosive, is shown in FIG. 6, where the number of registered gamma rays along the ordinate axis is given 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 weighing 200 g, shown in FIG. 7, where the number of registered gamma rays along the ordinate axis is given 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 entering the composition of the radiation protection material 8. Moreover, on the energy spectrum shown in FIG. 7, compared with the energy spectrum shown in FIG. 6, a relatively high number of registered gamma rays with an energy of about 10.8 MeV is observed, which is associated with the presence of 1 nitrogen-containing explosive in the controlled object.

Then, the computer 5, based on the obtained energy spectrum of the registered gamma radiation of the camera 9 with the controlled object 1 located in it, determines and stores the number N _{m of} registered gamma-rays with energies from 2.0 to 2.4 MeV, the number N _{P2 of} registered gamma-quanta with energies from 2.7 to 2.9 MeV and the number N _{P of} registered gamma rays with energies from 3.5 to 10.1 MeV. In the future, the computer 5 determines and stores the first, second and third correction factors in accordance with the expressions ki = N _P i / N _K i, k ₂ = Nпг / Nkg and k ₃ =

(Nпз / Nκз) ² .

Next, the computer 5, based on the obtained energy spectrum of the registered gamma radiation of the camera 9 with the controlled object 1 located therein, determines the number of registered gamma rays with energies from 9.2 to 10.2 MeV and the number of registered gamma rays with energies from 3.4 up to 7.7 MeV, calculates their ratio and compares the resulting ratio with a threshold value equal to, for example, 0.0007. As can be seen, comparing the energy spectra shown in FIG. 6 and 8, the presence of 75 g of chromium in the controlled object 1 (see Fig. 8) leads to a significant increase in the number of registered gamma rays with energies from 9.2 to 10.2 MeV compared to the number of gamma rays recorded in the same energy range when irradiated with thermal neutrons of the same controlled object 1 (see Fig. 6). At the same time, in the range of energy values from 3.4 to 7.7 MeV, the number of registered gamma rays has not changed (see Figs. 6 and 8). Similar results were experimentally obtained by the inventors for the case in the controlled subject 1 materials containing selenium and iron. In this regard, the value of the obtained ratio of the quantities of registered gamma-quanta in these energy spectrum ranges allows us to judge the presence or absence in the controlled subject 1 of materials containing these elements that can cause a false alarm.

Therefore, if the obtained ratio does not exceed the specified value, this means that in the controlled object 1 there are no nitrogen-free materials that, when irradiated with thermal neutrons, intensively emit gamma rays with energies close to 10.8 MeV, and therefore can cause false alarming. As noted above, such materials may be materials containing chromium, selenium or iron. In this case, it is advisable, without fear of false alarms, to select gamma rays with energies close to 10.8 MeV in a wider energy range, including a value of 10.8 MeV, for example, from 9.9 to 11.0 MeV.

Exceeding the indicated threshold value equal to 0.0007 by the obtained ratio indicates the presence in the controlled object 1 of nitrogen-free materials that, when irradiated with thermal neutrons, intensively emit gamma rays with energies close to 10.8 MeV, for example, chromium, selenium, or gland. In this case, to reduce the likelihood of a false alarm, it is advisable to select gamma rays with energies close to 10.8 MeV in a narrower energy range including a value of 10.8 MeV, for example, from 10.2 to 11.0 MeV, i.e. with a larger, for example, 3% lower boundary energy value. Computer 5 determines the estimated number of background gamma rays with an energy in the specified energy range, including the value of 10.8 MeV, recorded in the chamber 9 with the subject 1 controlled by thermal neutrons, in accordance with the expression Nph = kiNphi + k ₂ Nph ₂ + kzNfz + Nfk, where N _Ф i, N _Ф2 , N _фз - obtained at the stage of analysis of the energy spectrum of an empty chamber corresponding to the three background components indicated above of the number of registered background gamma-quanta with energies in the range from 9.9 to 1 1, 0 MeV or from 10.2 to 11, 0 MeV, selected by computer 5 depending on the result of the comparison performed in the previous step; N _ФК - obtained at the stage of calibration of the explosive detection system in a controlled object before putting it into operation and stored in computer memory 5, the number of background gamma-quanta due to the cosmic component with energies in the range of 9.9-11, 0 MeV or 10.2 -11.0 MeV, selected by computer 5 depending on the result of the previous comparison step.

Then, on the basis of the obtained energy spectrum of the registered gamma radiation of the camera 9 with a controlled object 1 located in it, computer 5 selects gamma quanta with energy located in a predetermined interval between the lower and upper boundary energy values, including a value of 10.8 MeV, and counts them number N. In this case, computer 5 calculates gamma rays with energies in the range of 9.9-11, 0 MeV or 10.2-11, 0 MeV, selected depending on the result of the comparison with a threshold value equal to 0.0007, the ratio to t he detected gamma rays with energies from 9.2 to 10.2 MeV to the amount of detected gamma-rays with energies from 3.4 to 7.7 MeV. To compare the number N of selected gamma quanta with the estimated number N _{f of} registered background gamma quanta with energy in a given range of energy values including 10.8 MeV, computer 5 calculates the logarithm of the likelihood ratio, for example, of the following form L = (NIn (I + N _o / Nф) -No), where N is the number of gamma-rays emitted with energy in a given interval between the lower and upper boundary energy values, including a value of 10.8 MeV; N ₀ - obtained experimentally during preliminary calibration, the number of detected gamma-quanta with a minimum detectable mass of gamma-quanta with energy in a given interval between the lower and upper boundary energy values, including a value of 10.8 MeV, recorded in the case of a controlled object 1 nitrogen-containing explosive; N _f - the estimated number of registered background gamma rays with energy in a predetermined range of energy values, including a value of 10.8 MeV. Then, the computer 5 compares the obtained logarithm L of the likelihood ratio with the lower and upper threshold values equal to L ₁ = ln ((1-P _P oV (1-Plt)) and L ₂ = ln (P _P o / Plt), respectively, where P _po - required the probability of correct detection of explosives in a controlled subject; P _L t - the required probability of false alarm. If, as a result of comparing the logarithm of the likelihood ratio, it turns out to be less than the lower threshold value L ₁ (bc), computer 5 gives a signal that there is no explosive in the controlled object 1 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 the logarithm of the likelihood ratio lies between the lower and upper threshold values C and L ₂ (L-ι <L <L ₂ ), continue monitoring by repeated neutron-radiation analysis of the controlled object with repeated irradiation with thermal neutrons, registration of gamma rays and re-decision, as provided by the claimed method and the system that implements it. If after such a second check it again turns out that a decision on the presence or absence of explosive in the controlled object 1 with the required probabilities of correct detection and false alarm cannot be made, computer 5 gives a signal about this to the alarm signaling device 6, indicating it to the system operator, and sends a signal to the drive of the conveyor 4, starting the conveyor 4. The conveyor 4 moves the controlled object 1 from the horizontal shaft 3 of the installation 2 for neutron radiation analysis and after the exit counter liruemogo object 1 from its horizontal shaft 3 is removed from the conveyor belt 4 and sent to the dissection and examination.

If gamma-quanta with energies in a given interval between the lower and upper energy limits including 10.8 MeV were extracted in a wider energy range from 9.9 to 11.0 MeV and, as a result of comparison, the logarithm L of the likelihood ratio will be greater than the upper threshold value L ₂ set for it (L> L ₂ ), computer 5 issues a signal about the presence of explosive in the controlled object 1 to the alarm signaling device b, indicating it to the system operator, and sends a signal to the transport drive RA 4, starting the 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 controlled object 1 leaves the horizontal shaft 3, it is removed from the conveyor belt 4 and sent for autopsy and visual inspection.

If the allocation of gamma rays with energy in a given the interval between the lower and upper boundary energy values, including the value of 10.8 MeV, was carried out in a narrower energy interval from 10.2 to 11, 0 MeV and, as a result of comparing the logarithm L, the likelihood ratio would be greater than the upper threshold value L ₂ set for it ( L> L ₂ ), computer 5 determines the ratio of the number N of selected gamma rays to the number of registered gamma rays with energies in the range from 9.6 to 10.2 MeV. Then, the computer 5 compares this obtained ratio with its upper and lower threshold values equal, for example, to 0.9 and 0.6, respectively. If this ratio lies between its upper and lower threshold values equal, for example, to 0.9 and 0.6, respectively, computer 5 issues a signal that there is no explosive in the controlled object 1 to the alarm signaling device 6, indicating it to the system operator, and gives a signal to the drive of the conveyor 4, starting the conveyor 4, and the controlled object 1 is removed from the control, leaving the conveyor 4 from the control zone.

When the specified ratio exceeds the upper threshold value, equal to, for example, 0.9, or when the specified ratio is less than the lower threshold value, equal to, for example, 0.6, the computer 5 gives a signal about the presence in the controlled object 1 of an explosive to the alarm 6 , indicating it to the system operator, and sends a signal to the drive of the conveyor 4, starting the conveyor 4. The conveyor 4 moves the controlled object 1 from the horizontal shaft 3 of the installation 2 for neutron radiation analysis and after the exit of cont the rolled object 1 from the horizontal shaft 3, it is removed from the conveyor belt 4 and an autopsy and a visual inspection are sent.

These materials confirm the possibility of implementing the present invention and solving the problem, which consists in reducing the likelihood of missed explosives and false alarms when detecting explosives. Industrial applicability

Tests of a prototype explosive detection system in a controlled object created in accordance with the present invention were carried out on the experimental basis of the applicant, and in early 2004 at the Pulkovo airport in St. Petersburg. The tests showed that it was possible in principle to detect modern nitrogen-containing explosives with a minimum mass of 100-200 g in the typical baggage of air passengers with the usual baggage density nitrogen nitrogen-containing materials that are not explosives, from 2.3 to 2.4 g / DM ³ . The experimentally estimated probability of the correct detection of an explosive of a minimum mass of 100 g 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

CLAIM

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, detecting emitted gamma rays, emitting gamma rays with energy located in a predetermined interval between the lower and upper boundary energy values, including a value of 10.8 MeV, counting the selected gamma rays, deciding on the presence of explosive material in a controlled object, when the number of gamma-quanta extracted exceeds the expected number of registered background gamma-quanta with energy in a predetermined energy range, including a value of 10.8 MeV, characterized in that before placing the controlled object, the camera is irradiated with thermal neutrons, the energy the spectrum of the detected gamma radiation of the camera in the gamma-ray energy range with an upper limit of at least 11 MeV, when irradiated, we control thermal neutrons determine the energy spectrum of the registered gamma radiation of a camera with a controlled object in the gamma-ray energy range with an upper limit of at least 11 MeV before deciding on the basis of a change in the energy spectrum of the registered gamma radiation of a camera with a controlled object with respect to the energy spectrum of the detected gamma radiation of the camera in at least one predetermined subband of energy of gamma rays is determined by At least one correction coefficient for the value of the number of detected background gamma-quanta with energy in a given energy range including 10.8 MeV obtained by thermal neutron irradiation of the camera, and the estimated number of cameras with a controlled object detected during thermal neutron irradiation is determined background gamma-quanta with energy in a given range of energy values, including a value of 10.8 MeV, by multiplying by the correction ny coefficient obtained upon irradiation by thermal neutrons camera values of registered background gamma rays with an energy which is in a predetermined range of energy values comprising the value of 10.8 MeV.

2. The method according to p. 1, characterized in that the correction factor determined in the form of the ratio of the amounts of gamma quanta detected during irradiation of the camera with a controlled object and during irradiation of the camera and having energy values belonging to a given subband including a value of 2.23 MeV.

3. The method according to p. 1, characterized in that the correction factor is determined as the ratio of the numbers of gamma rays detected when the camera is irradiated with a controlled object and when the camera is irradiated and has energy values belonging to a given subband, including a value of 2.8 MeV.

4. The method according to p. 1, characterized in that the correction factor is determined as a square of the ratio of the number of gamma quanta detected by irradiating the camera with a controlled object and by irradiating the camera and having energy values belonging to a given subrange from 3.5 to 10, 1 MeV.

5. The method according to p. 1, characterized in that when irradiating a camera with a controlled object in case of exceeding the ratio of the number of registered gamma rays with energies from 9.2 to 10.2 MeV to the number of registered gamma rays with energies from 3.4 up to 7.7 MeV of its threshold value, the lower boundary energy value of a given energy range, including a value of 10.8 MeV, is increased.

6. The method according to p. 5, characterized in that after increasing the lower boundary value of the energy of a given energy range, including a value of 10.8 MeV, if the number of selected gamma quanta exceeds the expected number of registered background gamma quanta with energy located in a given the range of energy values, including the value of 10.8 MeV, determine the ratio of the number of gamma rays emitted to the number of registered gamma rays with energies from 9.6 to 10.2 MeV and decide whether explosive substances in a controlled object based on a comparison of the relationship with his two thresholds.

7. The method according to p. 6, characterized in that they decide on the presence of an explosive in a controlled object when the ratio of the number of gamma rays emitted to the number of registered gamma rays with energies from 9.6 to 10.2 MeV exceeds a threshold value.

8. The method according to p. 6, characterized in that they decide on the presence of explosives in the controlled subject in excess the lower threshold value of the ratio of the number of selected gamma rays to the number of registered gamma rays with energies from 9.6 to 10.2 MeV.