Inspection system and method for identifying substance components of an

Abstract

The proposed invention comprises a device for obtaining a radiographic image in backscattered radiation and a method for determining a substance composition of an object to be inspected. The apparatus includes an X-ray source with a mechanical scanning system, a detection system, a processor unit, and a radiographic image display device. The detection system of the system is formed by an array of NaI (T1)-based scintillation spectrometers and has a large total sensitive surface area. Maximum reduction of the number of array elements is achieved by coupling scintillation crystals and photodetectors through a light guide. A substance composition is identified by comparing the measured energy distribution with a reference value, and the substance composition is displayed on a radiographic image using pixel color coding. The technical result achieved with the claimed invention consists in increasing the radiographic image information content and significantly expanding its functionality, which allows people to identify and display its material composition in the form of a specific image while obtaining a radiographic image of an object to be inspected.

Description

Technical Field

[0001] The claimed group of inventions relates to an X-ray inspection system designed to detect objects hidden behind an optically opaque barrier. Background Art

[0002] In X-ray inspection systems, there are devices where the X-ray emitter and the detection system are located on the same side relative to the object being inspected. In such inspection systems, the surface of the object being inspected is scanned by a pencil X-ray beam, and the intensity of the radiation scattered (reflected) by the object is recorded by the detection system synchronously with the displacement of the detection beam and used to produce a radiographic image. This type of detection system can be designed in both mobile and fixed form and is generally referred to as "backscatter" [1]、[2] .

[0003] In such inspection systems, a radiographic image of the inspected object is generated based on the measured intensity of the backscattered radiation. The image contrast is determined by the material composition of the object and the specific geometry of each region of the object, for example, by the extent of the region along the direction of the detection beam. For this reason, the material composition of the object can never be determined solely from intensity measurements.

[0004] What is known is [3]、[4] , information about the material composition of each area of ​​the inspected object is obtained not only through the intensity of the scattered radiation, but also through the energy spectrum of the scattered radiation.

[0005] Indeed, an inspection system capable of measuring not only the intensity but also the energy spectrum of the scattered radiation provides relevant information for identifying the material composition of each region of the inspected object.

[0006] In the following, the term "inspected object area" denotes the section of the object that is illuminated by the detection radiation beam during the exposure time of one picture element (pixel). Differentiating the substance of the object involves identifying the substance in each pixel.

[0007] In the prior art, there are systems and methods for determining the relative positions of materials with high atomic numbers and low atomic numbers relative to a detection beam based on energy spectrum analysis of backscattered radiation. [3]. The inspection system scans the inspected object with a pencil X-ray beam, the radiation scattered by the object being recorded by two sensors which have different sensitivities to the high-energy and low-energy parts of the energy spectrum. The method for determining the relative position of the material is based on the fact that the combination of the signals of the two sensors allows one to roughly estimate the energy characteristics of the scattered radiation and to infer as a final result the relative position of materials with high and low effective atomic numbers along a specific line of sight. This conclusion is based on the fact that the energy spectrum of the backscattered radiation varies depending on whether an object with a low atomic number (low-Z) is located behind a layer of material with a high atomic number (high-Z) or, on the contrary, in front of it.

[0008] These systems and methods known from the prior art do not provide sufficient information, since they do not allow the material composition of the objects to be identified, but can only infer the relative position of objects with significantly different atomic numbers. The estimation of the energy signature of the scattered radiation is based solely on a comparison of its two parts (high-energy and low-energy), which is therefore too rough and does not allow the material composition to be identified. The known methods are not sufficiently sensitive to changes in the energy spectrum due to the material composition of the objects, which is additionally demonstrated by the necessity shown in the present invention to take into account the absorption in the air.

[0009] A system and method for determining the atomic number of a substance of an object under inspection are known in the prior art, which, apart from the functions claimed therein, are closest to the claimed invention in terms of technical solution and operating principle and are used as a prototype [4] . Summary of the invention

[0010] The inspection system of the invention is an X-ray mobile inspection complex comprising at least one sensor for determining the distance from the detector to the surface of the object and a set of inorganic scintillation detectors (e.g. NaI(Tl)) or organic scintillation detectors (e.g. polyvinyltoluene), each of which is coupled to one or more photosensitive readers, such as photomultiplier tubes or photodiodes. In exactly the same device, it is proposed to use as an option several detectors based on high purity germanium HPGe or on wide bandgap dielectrics such as CdTe, CdZnTe, HgI, etc.

[0011] The signals from a set of detectors are fed to an analog-to-digital converter (ADC) and then to a processor which processes the obtained radiographic image using a specific distance from the surface of the object to obtain the atomic number of the substance contained in the object.

[0012] The main disadvantage of the known devices is that, in order to obtain the desired result, the inspection system requires an unacceptably long time to identify the material composition of the inspected object.

[0013] The reason is that the signals from a group of detectors are transmitted to a single analog-to-digital converter (ADC). Such a technical solution fundamentally limits the speed of a group of detectors to the speed of a single detector in it. Among the detectors listed in the device, only the polyethylene toluene detector has a high speed, but the energy resolution of this detector is extremely low, which makes it unsuitable for spectroscopy. The spectral characteristics of other types of detectors described in the prototype are good enough for spectroscopy, but the speed of any of them is not enough to be used in the inspection system. DETAILED DESCRIPTION

[0014] In domestic and foreign scientific and technological literature, a special glossary related to the ionizing radiation field parameter measurement process has been formed so far.

[0015] Terms used in the claimed invention:

[0016] Detector (of ionizing radiation) - a sensitive element designed to convert ionizing radiation energy into another form of energy for recording or further conversion and / or measurement of one or more measuring instruments representative of the amount of radiation affecting the detector.

[0017] Scintillation detector (of ionizing radiation) - a radioluminescence detector that uses a substance that emits photons when exposed to ionizing radiation.

[0018] Ionizing Radiation (Energy) Spectrometer - a device designed to measure the energy distribution of an ionizing radiation field.

[0019] (Energy) scintillation spectrometer - a spectrometer that uses a scintillation detector as the sensitive element.

[0020] The claimed method for identifying the material composition of an object under inspection comprises: for an energy spectrum measured by a set of detectors, calculating values ​​of average energy and standard deviation, comparing them with a predetermined scale, wherein, as described in the prototype, low resulting values ​​correspond to substances with low Z, and high resulting values ​​correspond to substances with high Z. A disadvantage of the known method is that the energy signature of the backscattered radiation spectrum of heavy elements is non-monotonically related to their atomic number due to the significant contribution of their characteristic radiation. Therefore, the claim that "low resulting values ​​correspond to low Z substances, and high resulting values ​​correspond to high Z substances" is generally incorrect.

[0021] The detection system of the known device comprises a set of inorganic scintillation detectors (e.g. NaI(Tl)) or organic scintillation detectors (e.g. polyvinyl toluene), each of which is coupled to one or more photodetectors, such as photomultiplier tubes or photodiodes. The signals from the set of detectors are fed to an analog-to-digital converter (ADC) and then to a processor which processes the radiographic image obtained with a specific distance from the surface of the object in order to obtain the atomic number of the substance constituting the object. In the prototype, as an option, it is proposed to use a set of detectors based on high purity germanium HPGe or on wide bandgap dielectrics such as CdTe, CdZnTe, HgI, etc., and it is proposed to carry out, for each pixel of the image, the identification of the atomic number of the substance based on the calculation of the mean value and the standard deviation of the measured energy spectrum of the backscattered radiation and to compare the calculated results with a predetermined scale, in which their low values ​​correspond to low-Z substances and their high values ​​to high-Z substances.

[0022] The main disadvantage of the prototype is that it does not allow to identify the material composition of the inspected object with sufficiently high accuracy for the following reasons:

[0023] 1. The polyvinyltoluene used therein is characterized in that its photoelectric effect cross section is too small like any other organic scintillating substance, so it has an extremely low energy resolution, and,

[0024] For this reason, it is essentially unsuitable as a detector for scintillation spectrometers in the (20-160) keV energy range;

[0025] 2. The detectors mentioned in the patent based on wide bandgap dielectrics CdTe, CdZnTe, HgI, etc. have been known for decades, but are mainly used in laboratory practice. This is because the parameters of such detectors are not stable enough and the area of ​​their sensitive surface does not exceed 1 cm 2 These limitations are related to fundamental reasons and are well known to experts. In addition, tens of thousands of such detectors are needed to build a detection system with a large sensitive surface area.

[0026] 3. The HPGe based detectors used can only operate at liquid nitrogen temperature. The maximum area of ​​the sensitive surface of such detectors designed to operate in the energy range below 200 keV does not exceed 10 cm 2 , whose detection efficiency is less than 10% and costs tens of thousands of dollars. The main advantage of this detector over other types of detectors is its very high energy resolution, less than one percent. Using thousands of such detectors for continuous X-ray spectrometry is impractical.

[0027] 4. The signal transmission principle adopted from a group of NaI(Tl) detectors to a single analog-to-digital converter (ADC) is not suitable for total count rates above 10 6 At high count rates, the individual signals "overlap" each other, so that the amplitude of each signal cannot be determined, which makes the use of multiple detectors for scattered radiation spectrometry meaningless.

[0028] 5. The shown possibility of determining the atomic number of a substance and the accuracy of its identification has not been disclosed.

[0029] 6. According to the applicant, the statement that low result values ​​correspond to substances with low Z and high result values ​​to substances with high Z is also incorrect, since it is known that the average energy of the backscattered radiation spectrum of heavy elements depends non-monotonically on their atomic number due to the significant contribution of their characteristic radiation.

[0030] The claimed inspection system and method for identifying the composition of a material are based on the basic knowledge that the energy dependence of the absorption and scattering of X-ray radiation is unique for each material and that this manifests itself both in the intensity and in the energy spectrum of the scattered radiation of the inspected object. The claimed inspection system differs from known systems in that the detection system of the former together with the signal processing technology of the system allows one to identify the material composition of the inspected object in addition to allowing the construction of a radiographic image.

[0031] In order to solve most problems that arise during inspection, it is sufficient to have a boundary energy of (200-250) keV for the detection radiation beam of the X-ray radiation of the radiation source. In this case, the maximum energy of the backscattered radiation quantum does not exceed (150-160) keV. Quantums with energies below (20-30) keV are strongly absorbed in the air and structural materials of the detection system and provide limited information about the inspected object. Therefore, the detection system of the inspection system must ensure the recording of backscattered X-ray radiation in the energy range of (20-160) keV.

[0032] The information content of a radiographic image increases with the number of scattered radiation quanta recorded by the detection system. However, this number of quanta, which is proportional to the intensity of the detection X-ray beam, is limited by the maximum permissible radiation dose to the object. In practice, this means that, assuming a characteristic distance of (1-1.5) m between the inspection system and the object and a typical displacement speed of the inspection unit relative to the object of (5-10) km / h, the maximum flux density of scattered radiation on the surface of the detection system will be about 10 7 1 / m 2 s.

[0033] The main flux of backscattered radiation generated by the detection radiation beam and directed to the emitter and detection system is within a solid angle of (1-1.5) steradians. The optimal area of ​​the sensitive surface of the detection system can be estimated to be (1-2) m 2 , which ensures that radiation scattered within this solid angle is detected.

[0034] In order to obtain the best quality radiographic images, the detection system as part of the detection equipment must not only have a sufficient area but also ensure high efficiency in recording X-ray quanta in the (20-160) keV range.

[0035] In addition, the detection system must be such that Co 57 A spectrometer with an energy resolution of at least 20% for the 122 keV line of the radioisotope source to allow identification of the material composition of the object.

[0036] The claimed group of inventions (inspection system and method for identifying the material composition of an inspected object) does not have the disadvantages indicated.

[0037] The technical results achieved by the claimed invention consist in increasing the information content of radiographic images and extending their functionality, which allows identifying and displaying the material composition of an inspected object in the form of a specific image and obtaining a radiographic image thereof.

[0038] According to the claimed invention, the listed technical results are achieved due to the fact that the examination system comprises an X-ray source with a mechanical system for scanning an object with a pencil beam of X-ray radiation, a processor unit, a device for displaying a radiographic image and a backscatter radiation recording system located next to the source, the backscatter radiation recording system consisting of a detector array, each element of which is made into a scintillation spectrometer, which for Co 57 The 122keV line of the radioisotope source has an energy resolution of at least 20% and an X-ray detection efficiency of at least 80% in the 30-150keV energy range, and comprises a NaI(Tl) scintillation detector, a photodetector, an electronic path, an amplitude analyzer for converting the scintillation signal sequence into a digital code sequence, and an interface for providing transmission of the digital code from each element of the array to a processor unit in synchronization with the formation of pixels of a radiographic image during scanning of the surface of the inspected object with the detection X-ray beam.

[0039] Furthermore, the technical results listed are achieved due to the fact that the sensitive surface area of ​​the recording system has a value covering the X-ray flux scattered by the object in the direction of the emitter within a solid angle of at least 1-1.5 steradians.

[0040] Furthermore, the technical results listed are made possible by the fact that the sensitive surface area of ​​each element of the spectrometer array is such that the flux of backscattered radiation quanta never exceeds (2-4)·10 5 / s.

[0041] Meanwhile, the technical results listed are achieved by coupling the NaI(Tl) scintillation detector of each spectrometer of the recording system to its photodetector through a light guide, which enables consistent collection of scintillation flashes from any point of the NaI(Tl) detector.

[0042] The listed technical results are also achieved by the claimed method for identifying the material composition of an inspected object, which method comprises measuring the energy distribution of the backscattered radiation synchronously with the formation of pixels of a radiographic image, and then comparing the measurement result for each image pixel with each reference database result available in a processor unit, wherein, according to the claimed invention, for each comparison, a Pearson "Chi-square" goodness-of-fit criterion is calculated, the minimum value of which determines whether the material of a given pixel belongs to one material group or to another material group.

[0043] In order to ensure the basic possibility of identifying the material composition of the inspected object, the inspection system should include (1-2)m 2 The invention provides a detection system with a sensitive surface area of ​​1000 m, which has a high X-ray radiation detection efficiency in the (20-160) keV energy range and can detect X-ray radiation with a detection rate of at least 10 7 A count rate of 1 / s measures such a radiation energy spectrum. The combination of these parameters of the detection system is also necessary to ensure statistical significance of the features of the recorded backscattered radiation.

[0044] In the above-mentioned (20-160) keV energy range, detectors based on inorganic scintillating materials are able to provide detection efficiencies close to 100%. Based on a combination of properties such as high atomic number, speed, high conversion efficiency, transparency to intrinsic radiation, cost, availability of large area samples, etc., NaI(Tl) is the optimal material for the detection system. This material is widely used in the construction of X-ray spectrometers and is well known to those skilled in the art. In order to ensure a detection efficiency close to 100% in the energy range below 150 keV, it is sufficient to use a NaI(Tl) crystal with a thickness of at least 10 mm.

[0045] Since the maximum radiation flux density on the surface of the detection system can reach 10 7 ·1 / (m 2 ·s), and the maximum count rate of the spectrometer using the NaI(Tl) detector does not exceed (2-4)·10 5 1 / s, so it is possible to measure the spectral components of X-rays with a high detection efficiency.2 The detection system for inspection systems with sensitive surfaces of 200 mm or larger should be a scintillation spectrometer array based on NaI(Tl) detectors. The number of elements of the array is selected so that the maximum flux of radiation quanta detected on the sensitive surface of each element does not exceed (2-4)·10 5 1 / s. This condition limits the maximum area of ​​the sensitive surface of the spectrometer to (300-400) cm 2 .

[0046] The detection system of the claimed system is an array of NaI(Tl) based scintillation spectrometers which are combined into a single system (see Figure 1 1 ). Each spectrometer (1) included in the detection system is connected to an interface unit (2). A rotary encoder (3) of the mechanism for forming a pencil-shaped X-ray beam is also connected to the interface unit (2). A processor unit (4) is connected to the interface unit (2).

[0047] exist Figure 2 The design of a scintillation spectrometer (1) is schematically shown in FIG. , which is a single element of the detection system.

[0048] The scintillation detector (5) is in optical contact with the photomultiplier tube (6). The output of the photomultiplier tube is connected to the input of an electronic path (7) designed to amplify the amplitude of the pulse signal from the output of the photomultiplier tube. The output of the electronic path is connected to the input of an amplitude analyzer (8). The amplitude analyzer is designed to convert the amplitude of each pulse signal into a digital code proportional to the amplitude. Figure 2 Other functional units of a typical scintillation spectrometer, such as a control unit, communication link transceiver, power supply, etc., are not explicitly shown in the figure, because their operation and detailed description of the specific implementation are not important for the claimed device.

[0049] The operation of the claimed device proceeds as follows.

[0050] The X-ray quanta interact with the working material of the detector (5) and produce a flash in it, which is proportional to the energy released in the detector. The photodetector (6) converts the flash into an electrical pulse. The duration of this pulse is determined by the duration of the flash, and its amplitude is proportional to the amplitude of the flash. The electrical pulse is amplified by the electronic path (7) and fed to the input of the amplitude analyzer (8). The amplitude analyzer converts the amplitude of each pulse signal into a digital code proportional to the amplitude of the signal. The digital code is transmitted to the output of the spectrometer (1).

[0051] The rotary encoder (3) of the device for scanning an object with a detection X-ray beam generates a logical electrical signal, which is determined by the direction of the detection X-ray beam at each moment. The signals from the rotation angle sensor are transmitted to the processor unit (4) through the interface unit (2). The processor unit (4) continuously generates continuous time intervals corresponding to the scanning cycle of a single element of the inspected object (pixel of the radiographic image) while receiving these signals. Each digital code from any spectrometer (1) enters the processor unit (4) independently of each other through the interface unit (2). A set of digital codes accumulated in the processor unit (4) during the scanning of each pixel of the radiographic image is an energy spectrum for identifying the material composition of each element of the inspected object.

[0052] Figure 1 The maximum count rate of the detection system shown is equal to the sum of the limiting count rates of the spectrometers contained in the system. At the same time, the limiting count rate of each spectrometer (1) is limited by the operating speed of the amplitude analyzer (8) located in the spectrometer. Whether the amplitude analyzer is implemented by circuit or by software, the speed of the amplitude analyzer is in turn limited by the duration of the flashes in the detector, which limits the maximum count rate of the entire spectrometer. For a spectrometer using a NaI(Tl) detector, the limiting count rate does not exceed (2-4)·10, no matter how large the sensitive surface area of ​​the detector is. 5 1 / s.

[0053] Furthermore, the above result is achieved in that the sensitive surface area of ​​the detection system of the examination unit covers the X-ray flux scattered by the object in the direction of the emitter within a solid angle of at least 1-1.5 steradians.

[0054] Furthermore, the claimed technical result is achieved by the fact that for Co 57 The 122keV line of the radioisotope source forms an energy resolution of each of the scintillation spectrometers of the detection system of not less than 20%, and the X-ray detection efficiency is at least 80% in the energy range of 30-150keV.

[0055] Furthermore, the technical results listed are achieved by optimizing the energy resolution and sensitive surface area of ​​the spectrometer included in the detection system. The best energy resolution is achieved in the scintillation spectrometer if the area of ​​the output surface of the scintillation device does not exceed the area of ​​the sensitive surface of the photodetector. In this case, for a NaI(Tl) crystal coupled to a photomultiplier, a typical value of the energy resolution measured for the 122keV line can reach (8.5-9)%.

[0056] The maximum sensitive surface area of ​​industrially produced photodetectors (photomultipliers) does not exceed 200 cm 2, which is significantly smaller than the maximum permissible area of ​​the sensitive surface of a single element of the detection system (300-400) cm 2 Direct coupling of a scintillation detector (5) having an area significantly larger than the sensitive surface of the photomultiplier tube (6) Figure 3 a) leads to significant inhomogeneity of the scintillation signal over the spectrometer surface, resulting in an unacceptable reduction in energy resolution. Reducing the sensitive surface of the scintillation crystal to the size of the sensitive surface of the photodetector leads to an increase in the total number of spectrometers in the detection system and thus to a significant increase in the cost of the system.

[0057] The number of spectrometers in the detection system can be optimized by coupling a large area scintillation detector (5) to the photodetector (6) via a light guide (9). Figure 3 b) Although the amplitude of the scintillation signal is reduced during the use of the light guide, the light guide provides better uniformity of the scintillation signal over the entire area of ​​the detector and reduces the degradation of energy resolution due to the use of a large detector area.

[0058] The area of ​​the input surface of the light guide should not be smaller than the area of ​​the exit surface of the scintillator, and the area of ​​the exit surface of the light guide should not exceed the area of ​​the sensitive surface of the photodetector.

[0059] Figure 4 Curve (10) in shows the inhomogeneity that occurs when a NaI(Tl) detector with a diameter of 200 mm is coupled to a photodetector with a diameter of 160 mm.

[0060] Figure 4 Curve (11) in shows the improvement in uniformity due to the use of a light guide.

[0061] By judicious choice of the detector to photodetector area ratio and the size of the light guide, the number of spectrometers in the detection system can be reduced to an acceptable number of (20-30) while maintaining the energy resolution at an acceptable level - no less than 20% for the 122 keV line.

[0062] The technical result achieved in the claimed device is also achieved by a method for identifying the material composition of an inspected object.

[0063] For each pixel of the radiographic image of the object, Figure 1 The energy distributions accumulated in the processing unit (4) shown carry information about the material composition of the pixels, but the statistical significance of these distributions is not sufficient to determine the material with an accuracy of one atomic number.

[0064] The low statistical significance of the measurement results does not allow to distinguish between substances with similar atomic numbers, but leaves the possibility of distinguishing between groups of substances such as organic substances, inorganic substances and heavy metals.

[0065] For each of these substance groups, calibration measurements are performed using known substances. The average results of the calibration measurements are assigned to a reference database, stored in the processor unit of the detection system, and used to evaluate the measurement results.

[0066] The material composition of each pixel of the radiographic image of the object is identified by a non-parametric method of statistical hypothesis testing, which consists in comparing the measurement result with each library reference value and calculating the Pearson "Chi-square" goodness-of-fit criterion for each reference value. Based on the value of the goodness-of-fit criterion, for a given significance level, a conclusion is drawn about the probability that the material of a given pixel belongs to one material group or another.

[0067] The digital code of the identified substance group is assigned to the pixel together with a digital code proportional to the intensity of the detected radiation. When visualizing a radiographic image of the object, the brightness of the pixel is proportional to the intensity of the radiation and its hue is determined by the digital code of the identified substance group.

[0068] An experimental verification of the claimed method for identifying the material composition of an inspected object was carried out on a prototype of the claimed inspection system having a total area of ​​0.7 m 2 The X-ray tubes were supplied with 225 kV during all measurements.

[0069] To generate the reference database, test samples made of polystyrene, aluminum alloy, steel, tungsten and lead were measured. The test samples were placed 1.5 meters away from the inspection system and moved relative to the system at different speeds in the range of (1.5-3) m / s. Figure 5 The reference energy distribution measured for each material is shown in Figure 10. 6 In this figure, curve (12) corresponds to the polystyrene test sample, curve (13) corresponds to the aluminum alloy test sample, curve (14) corresponds to the steel test sample, curve (15) corresponds to the tungsten test sample, and curve (16) corresponds to the lead test sample.

[0070] Table 1 summarizes the Figure 5 The energy distribution shown is the average value calculated. The table shows that the average energy on the spectrum varies non-monotonically depending on the atomic number of the substance. Table 1. Average energy of the backscattered spectrum depending on the substance of the test sample

[0071]

[0072] The identification of the composition of matter using the claimed device and the claimed method was experimentally verified in a number of measurement series. In each of these series, a simulator of the object to be inspected was placed at a distance of (1-2) m from the detection system and moved relative to the detection system at a speed in the range of (1.5-3) m / s.

[0073] Implementation Method 1

[0074] The practical implementation of the claimed method for identifying the material composition of an object under inspection consists in placing plates of different thicknesses made of a specific substance (polystyrene or aluminum or steel or lead) on the surface of the object. The measurement results are automatically processed according to the claimed method. Regardless of the thickness of the plate, each substance is displayed on the radiographic image in its own color, which corresponds to each of the 3 determined groups of substances (organic substances, inorganic substances, heavy metals).

[0075] Implementation Method 2

[0076] This embodiment shows the implementation of the claimed method for identifying the material composition of an object under inspection, which is manifested by placing samples made of various substances (polystyrene, aluminum, steel, tungsten, lead) simultaneously on the surface of the object under inspection. On the radiographic image, each substance is displayed in its own color as a result of the performance of the claimed method.

[0077] Implementation 3

[0078] An embodiment of the claimed method for identifying the material composition of an inspected object, providing typical numerical results for the "Chi-square" goodness-of-fit criterion, averaged over 9 pixels of a radiographic image for each material, is shown in Table 2. These values ​​are obtained automatically according to the claimed method. Figure 5 The energy spectrum shown is used as a reference distribution, and the measurement results are taken from Embodiment 2.

[0079] Table 2. Values ​​of the "Chi-square" criterion

[0080]

[0081]

[0082] Table 2 shows that for each substance, the lowest goodness-of-fit criterion value corresponds to the case where the reference measurement is compared with a test sample taken from the same substance. This means that the test substance and the reference substance are identical, thus confirming that the claimed technical result allows one to identify the components of the substance under test by means of the claimed invention.

[0083] Implementation 4

[0084] This embodiment shows a practical implementation of the claimed method for identifying the material composition of an inspected object, which comprises a series of measurements with samples of polystyrene, wood, aluminium, steel, tungsten and lead, which are shielded from the detection X-ray beam by a 2 mm thick plastic sheet. On the radiographic image, each substance is displayed in a colour corresponding to the group to which it belongs in 3 selected groups (organic substances, inorganic substances, heavy metals).

[0085] List of information sources used

[0086] 1. Daniel J. Strom, W. Wade Sapp, and Josepf Callerame. Physics, health physics, and applications of backscattered X-ray imaging. PNNL-SA-36973.

[0087] 2. Swift RD Mobile X-ray Backscatter Imaging System for Vehicle Inspection / / Physics-Based Contraband Detection Technology - SPIE, 1997 - V.2936 - P.124-132.

[0088] 3. US8442186, B2

[0089] 4. WO2012109273A3 (prototype of the device and method)

[0090] Notice:

[0091] In domestic and foreign scientific literature, a list of special terms related to the measurement process of ionizing radiation field parameters has been formed.

[0092] Terms used in the claimed invention:

[0093] Detector (ionizing radiation) - a sensitive element of a measuring instrument used to convert the energy of ionizing radiation into another form of energy suitable for recording or further conversion and / or measurement of one or more quantities characteristic of the radiation affecting the detector.

[0094] Scintillation detector (ionizing radiation) - a radioluminescence detector that uses a material that emits photons when exposed to ionizing radiation.

[0095] ionizing radiation (energy) spectrometer - a device used to measure the energy distribution of an ionizing radiation field.

[0096] Scintillation spectrometer (energy spectrometer) - a spectrometer whose sensitive element is a scintillation detector.

Claims

1. An inspection system comprising an X-ray source with a mechanical device for scanning an object with a pencil beam of X-ray radiation, a processor unit, a device for displaying a radiographic image and a backscatter radiation recording system located next to the source, the system consisting of a detector array, wherein each element of the detector array is designed as a scintillation spectrometer, the scintillation spectrometer for Co 57 The 122keV line of the radioisotope source has an energy resolution of at least 20% and an X-ray detection efficiency of at least 80% in the 30-150keV energy range, and comprises a NaI(Tl) scintillation detector, a photodetector, an electronic path, an amplitude analyzer for converting the scintillation signal sequence into a digital code sequence, and an interface, which provides the transmission of the digital code from each element of the array to the processor unit synchronously with the formation of pixels of the radiographic image during scanning of the surface of the inspected object with the detection X-ray beam.

2. The inspection system of claim 1, wherein the recording system has a sensitive surface area that covers the X-ray flux scattered by the object toward the emitter within a solid angle of at least 1-1.5 steradians.

3. The inspection system of claim 2, wherein each element of the spectrometer array has a flux of backscattered radiation quanta that never exceeds (2-4)·10 5 / s sensitive surface area.

4. The inspection system according to claim 1, wherein the NaI(Tl) scintillation detector of each spectrometer of the recording system is coupled to its photodetector through a light guide, which enables uniform collection of scintillation flashes from any point of the NaI(Tl) detector.

5. A method for identifying the material composition of an object under inspection, comprising measuring the energy distribution of backscattered radiation synchronously with the formation of pixels of a radiographic image and then comparing the measurement result for each image pixel with each reference database result available in a processor unit, wherein For each comparison, the Pearson "Chi-square" goodness-of-fit criterion is calculated, the minimum value of which determines whether the substance at a given pixel belongs to one substance group or the other.

Images